"Muse" Voyager S06E22.

It would be so meta because it's already an episode doing a play in an amphitheater.

My first thought was TNG 'Frame of Mind' for the delicious meta, but I don't know how that would actually work. I think Measure of a Man is a great choice. Courtroom drama tends to play well on stage. Any other courtroom episode could be worth a look too. TNG 'The Drumhead' and SNW 'Ad Astra Per Aspera' come to mind.

"Waltz" from DS9 would work really well I think. If you cut out the b plot of trying to find sisko, you only need 5 actors, and it takes place in one cave. You could probably get away with one set, maybe two or three props, and no practical effects.

TOS: The Conscience of the King. The script feels like a stage play. There are no space battles or other big set pieces. It’s just people talking in different settings but it’s a gripping drama.

I think both Darmok and The Inner Light from TNG would be solid candidates. Both are more about the story and dialogue than the setting, and while both have more sets than OP's examples, there's also plenty of room to consolidate and move scenes around. Almost all of the stuff on the planet in both episodes, for example, could be a single set with just a few pieces of furniture (or rocks) moving around to give the allusion of location changes.

They are also very good episodes that have a message beyond just the setting and plot, which make for a good play, as well.

How about DS9's "The Wire". A powerful story of isolation, suffering, addiction, and the power of friendship coupled with medical professionalism. I have to admit I don't recall anyone else's role other than Dr. Bashir's and Garak's (and some momentary spots with Quark and some random nurse). I don't remember what the B plot was.

"Spock's Brain" actually was licensed and performed by a community theater as a comedy. The teaser and part of the first act used to be on YouTube.

"Remember Me" could make for an interesting (almost) one-person show.

TOS “The Empath”

"Spectre of the Gun" has a pretty surreal set and I could easily imagine it as a play.

"Duet", as it's a loose adaptation of the play (originally novel and later also film) The Man in the Glass Booth.

Legal procedure episodes work well as stage plays, The Cane Mutiny was a play before becoming a feature film.

So we got Court Martial, The Menagerie, Measure of a Man, The Drumhead, Devil's Due, Tribunal, Rules of Engagement, and Ad Astra per Aspera.

Throwing Voyager’s ‘The Thaw’ into the mix.

It’s definitely a polarizing episode, but I think it’s one of the strongest. It’s a better adaptation of the premise of Stephen King’s novel ‘It’ than many others.

The episode itself is primarily staged in an artificial environment that would lend itself well to a theatre set. It might be possible to reduce the number of sets on Voyager itself to one.

TNG’s ‘The Most Toys’ likewise principally takes place in a single room.

What about DS9's In The Pale Moonlight or It's Only a Paper Moon?

Ballance of terror would be great, I'd stage it with both bridges on stage, with the view screens facing each other center stage. while the action is happening on the enterprise have the lights on the Romulan bridge at 15-20% and vise versa. My production would sacrifice the surprise reveal in favor of some scenes on the Romulan bridge in act 1.

Fascination would probably be fun. Or Dramatis Personae.

edit: oooh, how about Repression?? Pagh t'em far, B'tanay!