At what point in the story do the couple become locked inside? (Beginning of second act?)
What is the objective or goal once they are trapped inside? Is it just to survive for 2 years? What is stopping them from doing that? (Presumably the biosphere is set up to handle 8 inhabitants? So I imagine there’d be plenty of supplies for 2 people trapped in there. Also, if they’re not actively trying to kill one another, and there’s no other antagonist, I’d say survival is pretty much assured. So what you have is 2 characters trapped in one location who dislike one another, but with no other objectives. So they’re just squabbling for the 90 min run time? I can’t imagine anyone would want to fund that film, much less see it).

I think there’s potential in the idea — the setup works for a low-budget kind of thing. But I agree with Nir; I think the premise needs work.

“After they’re sealed inside?their?biosphere experiment midway through a supply delivery, two?unscrupulous academics in a failing marriage must work together to survive the next 24 months.”

Trying that out, it makes me wonder; what is at stake if the experiment fails? That seems to provide the momentum for WHY they must tough it out, instead of just shut it down and escape.
Also — it feels like the repair of their relationship; and arc from distant to loving for the couple, is going to be central to the story. But I want to know, in the logline, what it is that might drive a wedge between them? Perhaps there are THREE people locked in there? (And this person can be used as the third point in a love triangle — perhaps, the third character is so spurned by the way they’re manipulated and used by the other two trying to get back at each other, that in the second half even becomes the antagonist; attempting to sabotage the experiment and kill them all before the end).

It feels more than a little “Bio-Dome”, but could have some of “The Martian” in there.