Edited after over a year with additional details.
Read around 1997:
In it, a man escapes slavery, gets to a space colony with deadly entrance tests, gets bitten by a mutated bug, develops superpowers, and uses them to overthrow a government.
Relatively soft sci-fi. It had an adult male as the protagonist and was told from only his point of view. I read it in Finnish, but it's likely it was translated from English. I don't remember any of the names, which probably means they were some basic English sci-fi names. The story was set maybe a few hundred years into the future, with space travel reasonably common. I don't remember if it was inside solar system. Most or all major characters were male.
Main character (MC) was a slave on a planet, probably Earth. I don't remember if he was born a slave or captured at some point.
Each slave had a device in them, which the owner could use to cause pain if they wanted, using a remote.
One of the other male slaves slept with the owner's wife (or concubine or something like that), and was punished by the owner by some extreme humiliation that happened offscreen. The friend then killed himself out of shame, and the owner contemplated that as an older man he hadn't remembered that a younger man might kill himself when he lost his pride.
Another slave had tried to escape, but was caught. He was killed by his slave device, by causing pain until his heart gave out. The other slaves were forced to listen, I remember the main character closed his eyes and tried to solve some mathematical problems in his head to not listen to the screams.
MC escaped with some others, I think they either stole the remotes or ran away outside of the remote's range. They posed as androids on an airport to get to space, there was mention of no one paying attention to them since androids are just servants, someone even had him carry some stuff but never looked at him twice.
There was a colony in space (maybe on a habitable asteroid) that the slaves knew about, with deadly entrance tests that few survive. Everyone needed to do 3 tests: 2 random ones selected by pressing buttons, and a common last test for everyone. The MC spent a bit of time selecting which buttons to press even though he had no way to known what tests they led to, picking some colors with pleasant memories to him.
It was discussed that the entrance tests were designed to be so difficult that they would kill anyone with just a normal desire to not die, they wanted only extremely motivated people in the colony.
As one test, MC fought an android that was programmed to stop using limbs if they suffered damage that would break a human's limb, to make the fight just barely possible to win for a very determined human. It seemed that otherwise the android could have killed pretty much anyone. After winning, MC tried to attack the person who came to tell him he had won, and he was quickly sedated.
Another test was to climb a huge wall that was above some sort of heat source, possibly lava. The wall was reasonably easy to climb, but very very tall (probably took hours to climb, if not longer). MC took a piss into the lava before starting to climb, and thought about people who might be watching through cameras, and whether they would be excited about the pissing. Apparently some people wanted to see people fall to their death. There was a very long (or at least felt very long) description about the climb and how tiring it was toward the end. I think MC was given some salt to combat dehydration before the climb.
MC's friend had a test where he had protective gloves but was otherwise unprotected. There were some poisonous creatures coming from everywhere around him, and he needed to squish each one. Missing one would have most likely killed him with poison. This continued for hours. I don't think the book had any aliens in it, but the creatures also didn't seem like currently existing creatures on Earth. They might have had tentacles.
The characters in the colony considered what would happen if someone from Earth authority would come there with a lot of pain remotes and start triggering them to see if they match anyone in the colony, but didn't conclude whether the colony administration would stop them. So there was some sort of agreement between Earth and the colony, it was not hidden or in open war with Earth.
The third test for everyone was walking through some sort of mutated massive garden for days, with just barely enough supplies. Probably the plants and everything else was huge, and may have been some sort of accident originally (trying to grow better plants or something), then kept as a test location. Everything was supposed to be lethally poisonous. However, MC was bitten by some bug, got seriously ill but recovered and was able to complete the test. He didn't tell the colony leaders, probably because he was afraid of being turned into a lab animal.
There was mention that someone had been bitten or eaten something in the garden before, I'm not sure if they died or maybe survived but became insane or something, in any case they weren't participating in society anymore.
Later MC started gaining powers: telepathy, healing, putting people to sleep or killing them with his mind. He took others to the garden to be bitten by the bug, and they also gained the same powers. The colony allowed travel to the garden, apparently some colonists wanted to have revenge on some animals by coming back with proper weapons and equipment. They decided to fight the government that allowed the slave system to continue.
The slaves had some symbol or letter ("A"?) tattooed to their forehead. After getting the powers, MC's symbol started to fade after some days, and eventually disappeared. I think he considered that people would think he had been at some tattoo removal.
Another male friend of the MC was excited about the healing possibilites and wanted to cut off his finger to see if it would grow back, but the MC refused.
At one point MC used his mind reading powers to examine some woman in a cafe, there was a sort of stream of consciousness, from taste of food/drink to considering whether she'd like to have sex with the MC.
With the powers, the people could put people to sleep that only they could wake them from. At one point one of them walked the corridors of a hospital and woke up people they had put to sleep during some attack.
One government man was interrogated by the MC by asking questions and then reading the answer in his mind, then killed because MC wouldn't have been able to return to wake him up. MC thought that the man couldn't have been broken by traditional torture, but couldn't avoid the answers to questions coming to his mind to be read.
At the ending, MC let himself be captured by the government and posed as a messager who was only physically able to tell his message to the government's corrupted leader. Apparently there was some well known drug or treatment that would prevent messengers telling a message to anyone but the intended recipient. He was disarmed and pumped full of drugs (at least truth drug), but with his powers was able to kill all the guards anyway, and incapacitate the leader. I remember him being briefly concerned that the guards would have given him too much drugs, but was able to neutralize the drugs with his powers anyway.
He told the leader their plans, and the leader was considering orbital bombing to get rid of the threat of the powered people, then realized that the only reason he would tell him the plans, was because MC was going to kill him. Then MC did kill him. The book probably ended pretty quickly after that, I don't remember there being much about how the society handled after the evil government was overthrown.
There didn't seem to be any alien contact, only humans. I don't think aliens were discussed at all.
I don't remember the cover, but vaguely remember that it was likely largely black and softcover.
I tried going through mind power (telepathy etc.) related tropes on TV Tropes but couldn't find the book in any of them. It's frustrating that I'm able to remember so much of the book but I can't remember any names or anything that would be easy to search.