I launch GOG, I want to play Cyberpunk but there is only one option - INSTALL. My problem is I already installed the game and it is on my disc. i can run the game by finding the launch on my disc. However, I can't download a new patch and GOG doesn't count my playtime etc. and language is always restarting (Every time I need to change it in the settings).I thought about uninstalling GOG but I am afraid of my Cyberpunk's save.

There's a option keep your save in GOG Galaxy or you can just move your save files to a different folder.
user/saved games/CD Project Red/Cyberpunk 2077

I've just reinstalled GOG. It still claims Cyberpunk is not installed... I think I am forced to uninstall the entire game and install it again. I did backup of the files I found there.

-nvm-

On disk? If you bought a physical copy, my assumption would be: You don't have the game on that disk (1). I am not sure what and whats not included on those physical copies (soundtrack, extras)... So my best bet is: you installed galaxy, and galaxy needs to download the installer.... if you do not want to use galaxy: download the offline installer via galaxy (as you have it installed at the moment), or log in to gog via a web browser and download it from your library there.

[1] AFAIK no physical copy came with the offline installer.... I mean, over 100GB for the Offline Installer: what do you bought, a 4layer BD, 2 double layer BDs, 12+ DVDs????

Okay, I found a solution!!!

If GOG claims your game is not installed (but you know it is), you need to click Right Mouse Button on your game in your GOG library. Next click Manage Installation > Import Folder > choose a main folder of your game (for example folder "Cyberpunk 2077"). GOG will starts verifying/downloading/updating the game slowly and that's it.

My GOG version is 2.0 (GOG Galaxy)

This just saved me like...30 minutes. Thank you lol

I was having the same issue, but FireJach's solution wouldn't work for me... Everything under "Manage Installation," other than "Configure," was unselectable; And Configure is a dead end.

I got my game recognized as 'installed' like this:

1. Click gear icon in upper left corner
2. Go to "Add games & friends >"
3. Click on "Scan folders for GOG Games"
4. On the alert that pops up, choose "Select folder"
5.In the Windows explorer window that appears, choose the folder you want to scan.
Note: **I chose the "GOG Galaxy" folder in "Program Files (x86)," because I know the game's install folder is in there, and it will make the scan quicker by narrowing down the depth of the scan... but you could select "Windows (C:)" (or whatever drive letter you specified for install) directory if you're unsure where the default install location.**
6. Click "Select Folder" to scan.

:)

I had the same problem. I couldn't do it through 'manage installation', but your solution worked. Thanks!