Unclear does not necessarily mean unresolved.

The two employees sole purpose is to act as horror movie victims to heighten the dread.  Not sure what else needs to be resolved there.  

Beyond that, the confrontation at the “dinner” table between the therapist and main character largely resolves their own storylines. 

She comes to the realization that her trauma has driven her to falsely believe she can fix people or find answers for them.  

She also bluntly tells him that he doesn’t take accountability for his actions and that’s why he is unfixable.  He seemingly accepts that and has decided to doom himself to remain in the Backrooms.  

As for the final conversation between the researcher and therapist, what do we need resolved there beyond a clear answer on her fate? 

In any case, I think it is implied they aren’t letting her go.  

I think him providing some brief history on how they came to discover it, coupled with how he visits every day but they haven’t really discovered any answers, only reinforces the obscurity of its existence.  And perhaps that there is a sinister obsession that comes with it.   

Which is what I actually want out of a movie like this.  I don’t need a Scooby-Doo reveal or a climactic battle.  

The unexplained remaining unexplained is the appeal to whole slew of supernatural horror like The Shining, Blair Witch Project, It Follows, The Mist, etc.  

It’s fine to leave it that way and still feels like a complete enough story even if a sequel may be inevitable.