Coelacanth, 2 lata temu

Disco Elysium has a number of potential soft locks, though you kind of have to go out of your way to actually get into one. The easiest one is probably paying for your hostel room the second night. Usually a combination of decisions and unlucky dice rolls are necessary to actually get locked, and/or poor use of skill points (meaning you can’t spend one to re-try the crucial roll).

There is also a seemingly minor decision in a side quest that can make a certain check during the ending unwinnable and thus lock you out of one of the most impactful moments in the game.