Potential small spoiler, but I try not to be too specific, for those not knowing what it is about.

In the hotell basement, chapter 4 I think, I find that I need to light something, and from online walkthroughs I found out I am supposed to ask a person about that. But I will not get the apropriate dialog option, just the same old things.

Some page mentioned that you have to ask that question immediately after discovering the need, which I might not have done the first time, and repeating the step by looking at the thing needing light and then walking to and asking directly after does not help.

Have I "ruined" the game and need to replay everything from start? or is there a way past this to get that dialog option? or am I actually missing something else?
I have updated the game with gog galaxy and it sais version 1.5.

This is 6 years late but I am having the exact same problem. It's a shame because this is a beautiful game with a terrible game ending bug. Really ashame.

I'm hoping this post can help someone with this game. I can confirm there is a horrible game breaking bug and the only way to progress is to restart chapter 4 over. At the point where you have to make the schnapps. Open the door with Heinz's key (found in the swamp on his body) in Trude's hotel. After you go downstairs, collect everything you need. (The malt near the wall, the garbage can lid) Inspect the brewing machine and the hose. He will say he needs a light. Go back upstairs. IMPORTANT DO NOT EXIT THE HOTEL WITHOUT SPEAKING TO TRUDE AT THIS POINT OR YOU WILL SET OFF THE BUG. Talk to trude > Can I ask you something> Do you have a light? Should now appear.

If you want to continue this seems to be the only way. Don't forget to recollect everything and replay this chapter as if you just started it even if everything appears in your inventory. It will take an extra 20-25 minutes but if you want to play this seems to be the only way to get around the bug. Hope this might help someone.

Interesting, it seems I couldn't reproduce this bug. Just finished the game, so the memory is still fresh and I'm pretty sure I didn't ask Trude about the light. It didn't even occur to me I should ask anybody, so I went out in hopes that something has happened somewhere and I could find the item needed. It was merely a coincidence that I asked the boat rental lady on random and she had that option.

I'm not saying this bug doesn't exist, of course, but it's certainly not happening always.