Can all witches and wizards possess the ability to transform into an animagus or is it just the select few like Sirius Black (Padfoot) and Minerva McGonagall, for example.
In theory, they could if they had sufficient skill and practice. But most don’t.
The only bar to becoming an Animagus seems to be study and skill in Transfiguration:
Animagi make up a small fraction of the wizarding population. Achieving perfect, spontaneous human to animal transformation requires much study and practice, and many witches and wizards consider that their time might be better employed in other ways.
— Albus Dumbledore’s notes on Babbitty Rabbitty and her Cackling Stump
I’m not aware of any canon source which states that there are limits on who can become an Animagus, but as it states, most choose not too, because it’s a lot of effort for not a lot of utility.
So I think anybody could become an Animagus, but they don’t pursue it.
Indeed, we learn from Hermione that Animagi are very rare:
“I went and looked Professor McGonagall up on the register, and there have been only seven Animagi this century, and Pettigrew’s name wasn’t on the list—”
— Prisoner of Azkaban, chapter 18 (Moony, Wormtail, Padfoot, and Prongs)
Even if you throw in the four unregistered Animagi (the Marauders and Rita Skeeter), it still comes to a tiny fraction of the magical population.