What I am supposed to do? Since the start I pass the turns with Guard order (others are blackened), and nothing happens.
I thought it was a battle against the swamp&weather...

I guess it's a bug. Game broken, that's bad for a game where we can't save...

I'm having the same issue. For me it seems that every time an adversary manages to retreat, they'll be glitched the next time around, forcing you to abandon the run if you face them.
Just had my best run yet, and then this somehow happened with the final boss fight...

I read from steam forums that there's a fix for this, but we are a version behind on GOG it seems. I guess we can only wait.

Same, they pushed a fix on Steam. Developer Grendel stated 1.2.0.6 was pushed that fixed this on 12/18/2020, hopefully they fix this in a reasonable amount of time before I refund.

Got it too, i hope this fix will work retroactively. because right now, the only option is to start a new game.

Start a new game to go to this bug?
What a f... "deluxe" game...
I think I'll ask reimbursement soon, when GOG is ready

The update is out now. Seems to have fixed the problem for me. Didn't even have to abandon the run I had saved.

I had to: now I could see two enemies, but I still couldn't doing anything save defense.