I wonder if this might be a Zork spin-off/sequel called "Enchanter". Whether it was meant to be the fourth Zork game or not appears to have varied during development - see discussion at https://advgamer.blogspot.com/2017/08/missed-classic-enchanter-won-and-final.html
https://adventure.if-legends.org/Infocom.html includes "TRS-80 [Model I and III.]" and "TRS-80 Color" in their list of the machines it runs on.
If this is considered to be a Zork sequel, then you see your past self in a mirror early on in the game, but can't communicate with them. You need to find some way of bringing past/mirror you out of the mirror and into the present-day real world before the two/one of you can communicate.
It was one of those adventure games where you either typed commands in (e.g. "GO NORTH" "GET MIRROR" "SOLVE ASTROPHYSICS") or selected from a limited set of commands that essentially did the same thing of letting you pick a verb and an object.
It certainly was, though I don't have many screenshots to back that up and I don't think they're from the Tandy/TRS-80 version:
Without screenshots, I'll need to rely heavily on blog quotes for evidence:
The north end of the castle is a long hall of mirrors that reflect on
"another world". Sometimes, we can see an adventurer carrying an elvish
sword and lantern on the other side of the glass. It's a view to Zork!
I vaguely remember this puzzle from when I played as a kid and I think
there is some way to bring the adventurer to your side of the mirror but
I don't have any spell to do it quite yet or any idea why I would want
to do it."
Last week, I started my explorations of Enchanter by breaking into an
ancient castle inhabited by an evil warlock. It seemed to be going well
at first except I was too tired to memorize any spells, failed to find a
safe place to sleep, and then was captured by cultists and sacrificed on
an altar to a bloodthirsty god. I did manage to learn two new spells
(one to open doors and another to repair damaged objects), found a
mirror leading to the original Zork games, and encountered a door so
heavily guarded that its defenses had defenses.
As I head back to the entrance, I pass again through the Hall of
Mirrors. I mentioned this last week as the spot where I occasionally see
the adventurer from Zork. I can't seem to talk to him, knock on the
glass, or do anything else to get his attention yet and he doesn't even
always appear. I'll have to come back later.
Just as before, there is a tower in the corner but I pass it for now to
explore the southern hall. Roughly parallel to the Hall of Mirrors on
the other side of the castle is the Portrait Gallery, a hall containing
pictures of familiar faces including Dimwit Flathead (mentioned in Zork
I and encountered in III) and the Wizard of Frobozz (from Zork II).These
are the first real signs that this game takes place in the Zork
universe! I cannot find anything useful I can do with them so I move along
Next up, I'll try for the cartoonish man, whom I assume is the
adventurer in the mirror. I search and find him in one of the mirror
rooms and cast "zifmia" to summon him through. He's not very happy about
it! He is certainly "me" from the Zork series, down to the elvish sword
and trusty lamp, but he doesn't like "me" from the Enchanter series one
bit. With some experimentation, I find that I can cast "vaxum" on him to
get him to like me, but even then he just wanders aimlessly around the
castle picking up random odds and ends. I think I'm on the right track,
but what do I do next? I have no idea. (Incidentally, where does this
game have to fall on the Zork timeline? My guess is somehow between Zork
II and III since he knows about the Wizard of Frobozz but he still has
his sword with him. It can't be after III because then he'd be
transformed into the Dungeon Master. I probably am not supposed to think
too hard about this.)
I summon the adventurer and follow him around. He seems to always take a
fixed path around the castle at first, passing through the temple and
the hallway junction without incident. After that, he seems to go
aimlessly. If he sees any of my stuff lying around, he annoyingly picks
it up. He seems single-mindedly in pursuit of treasures like in the
first two Zork games.
In the process, I survived being sacrificed, watched a turtle be a ninja a full year before that would become a thing, and completely screwed up the Zork timeline by teleporting my character from the first games into an adventure that he wasn't expecting.
First up for this session, I need to work on the adventurer and the
guarded door. Since the last post, I'm fairly convinced that these are
one and the same puzzle: my dream (from two posts ago) showed a
cartoonish man opening a plain door. When I dispelled all of the magic
on the guarded door, it looked just as plain. It could be a coincidence,
but I doubt they would throw in such a great hint and not have it be the
correct solution. Each time I've cast that spell before, I did it while
I could see the adventurer in the mirror; this time, I go to the guarded
door and try the summoning spell from there except that doesn't work. It
says that I can summon a powerful magic-user without seeing him, but
everyday people can only be called if you can see them. That's good to
know! ... How can I get the adventurer to the door? I spent a while
following him last post and he never came to this room on his own.
The solution requires me to play off his (and, I suppose, my) inherent
greed: I show him the silver spoon and he starts to follow me around.
(Of course, I have to use "vaxum" to get him to like me first.) I lure
him to the guarded door and he doesn't seem to notice any of the
insanity there. I ask him to open the door and he looks at me like I've
grown a second head; he just walks over and opens it (ignoring boiling
lead poured on his head, attacking tentacles, and other magics which do
not seem to be real for him). When he's done, the illusions disappear
and I can see the plain door clearly. I follow the adventurer up the
stairs to reclaim the pencil, map, and "filfre" scroll. Since I didn’t
use "kulcad" to get in here, unlike the last time, I have it to use
someplace else. As I leave, the adventurer wanders off to explore the
castle on his own. Did I just break the Zork timeline? Do I need to
un-summon him somehow? Am I still thinking too hard about this?
They are thrilled that their ploy of sending someone completely
unqualified for the job worked and officially make me an Enchanter. I
win the game and never even pause to consider the poor adventurer that
I've left stranded in a Warlock's castle, very far from where he was
supposed to be.
As an aside, you stated:
Part of me wants to suggest that this was a port of a known series like Kings Quest
Well, Zork was certainly a very well known series indeed!