"Steam: Error accessing service", Error during publishing: Fail: [...] Result: k_EResultFail

I cannot upload to the workshop. It worked just fine a few months ago.

Whenever I try (no matter which configuration below I tried) it always does the same thing:

Give the error

"Publish failed | Steam: Error accessing service".

The game logs say this:

2024-04-25 05:10:52.930 - Thread: 1 -> Info: New workshop item with id 3231565535 created successfully.

2024-04-25 05:10:54.529 - Thread: 1 -> Error during publishing: Fail

2024-04-25 05:10:54.529 - Thread: 1 -> Info: Workshop item with id 3231565535 update finished. Result: k_EResultFail

I scoured every possible place on the internet and tried everything short of installing windows again.

What I tried (likely not a complete list):

• Uninstall steam
• Uninstall the game (multiple times)
• Verify integrity of game files
• Check Thumbnails (it has nothing to do with that)
• Delete any and all combinations of local cloud files and configs and saves
• Delete all online cloud blueprints (via Ctrl+F10; I have none currently)
• Start a new offline world, with a fresh config and try to upload a single block with no color
• Use only local blueprints
• Every combination of disabling steam cloud in steam itself or the game itself
• Contact steam support over this -- they told me to go to you.

I have a background in programming and about 1600 hours in this game, I kind of know what I am doing. And this is one of the few times googleing and researching did not lead me to fixing the issue; i don't start threads like this because I get frustrated after two minutes. I have been trying to fix this for like 2-3 days now. I am very motivated to help you solve this issue in whichever way I can. Give me debugging tools or whatever, ... but this state is just unacceptable.