Hi,

I post below for anyone who experienced same issue. In my case, i've found solution.

I was playing Noita yesterday for few hours. Today i go back home, wanting to play some more and i don't see game in \installed' category. Quick check and i found exe file is missing!

- Looks like every other file is in place.
- I've googled and this kind of problems seems to happen to other games too.
- Tried button 'install' in GOG Client and it throw E4 error, with description of permission denied for disk or that specific path.
- GOG and PC restart made Install button gray - inactive.
- I've googled some more and as recommended, turned off Anti Virus for 10 minutes to check if it helps. No success.
- I've run GOG Galaxy as Admin. No success.

I could not find any errors regarding this issue. No file in trash either.

I was about to uninstall and install the game, when i noticed that in Windows menu i see shortcut for Noita. So i click it.
Somehow it forced GOG to update Noita with no errors. Game run.
I've found that source of shortcut i've used is as follows:
"C:\Program Files (x86)\GOG Galaxy\GalaxyClient.exe" /command=runGame /gameId=<some_numbers> /path="D:\GOG Games\Noita"

After game launched GOG has issue with sync game with cloud, but i don't care right now.
It also turns out there was Noita update ;)
My saves are OK.

Best of luck
- F.

Update:

Turns out that avast at PC start moves exe file to quarantine. Today i have same situation as above, but this time i have notification, when 2 days ago - i had not.

Avast is a very bad anti virus software, remove it and use another anti virus (Windows Defender is proven to be the best free anti virus)

Agreed with NoxNebula. Avast is garbage antivirus software these days. It will let viruses and malicious softwars into your PC. Just use Windows own Defender. It does the job really well and it has never deleted a legit games EXE's.