Same experience here. But enough is enough and I asked GOG for refund.
I spent more than five hours trying to make this game work. Not a minute more. It’s a buggy mess. I’ll try again on six months.

Hello and thank you for your report. It's quite possible that the issue is related to the status of save files. Try backing up the files SavedGames and SavedFiles.info found inside the folder: Users/YOUR USER NAME/AppData/LocalLow/Cultic Games/Stygian, then erase those from the folder. Re-Launch the game and see if this activates the landing page. If yes, then it's certain that the save files don't work on the new patch as they should. If no, then problem lies elsewhere. Would you be so kind to report here once you've tried?

Erased the save files from the folder and launched the game offline to prevent the save sync and the menu still isn´t working.

Hello,
It's great that you react. As I wrote above, I have the same problem, so I guess it's probably not really unique problem.
I postponed the refund, because I REALLY want to play the game. My question is: Is it possible, that you patch it in the foreseeable future?

Is there any response to this question from the devs? I have the same problem on Ubuntu 18.04. Is the game given up by the devs????

I have the same problem. If the devs are not even able to make a working main menu then I have no hope that I might be able to enjoy the rest of the game in the unlikely case that this somehow gets fixed. This will be my first refund.

I have finally found out why the Main Menu in the linux version of the game is broken. Some files and folders under the "stygian/game/STYGIAN_Data/StreamingAssets/" directory are missing in the linux installer. You can fix this by copying ONLY the missing files from the windows version of the game. I tried to replace the whole folder but that resulted in a crash when starting the game.

Nevertheless i experienced many bugs in the form of broken quests etc. . One of them was the arkham stabber quest where the two mobsters at the crime scene just wouldn't show up, rendering the game unbeatable. I am not sure if this could have something to do with the files from the win version.

I have the same Problem with Ubuntu 20.04.
Will they ever fix the missing data on the Linux version...
Iam not sure if i want to spend hours trying out to fix it, because this should be done by the developers (its not like they released it yesterday) .
Who knows, maybe they will try to completely rework the whole game at some point, since so many people experience game-breaking bugs not only in the main menu - I would really love to see this working.

Maybe i will try adding the data from windows version as MajinBardok mentioned before at some point, but until then it gets my one star rev for not working at all.

Having the same issue here. I've heard it may have something to do with the Cultic Games folder being read-only, so I removed the flag but that didn't help.