I had this issue at first. Here is how I fixed it:

First, navigate the "More" drop-down menu and go to "Manage". Select "Uninstall" and make sure to delete all saved game data, etc. (Note: Im assuming you haven't played the game yet, therefore wont have any saved data).

I installed GOG Galaxy on my F drive and noticed that the download files were going to C drive.
On GOG Galaxy, there is a little Cog icon near the bottom-right corner. Click on it and you might see that "Install game to:", "Download games to:", and "Download extras to:" are all pointing to your C drive. I created the GOG Games folder, !Downloads folder, and temp folder on my F drive to directly mirror the setup that Galaxy created on my C drive. I think checked the "Manage all folders manually" box and pointed all 3 locations to my newly created folders on my F drive, the same drive where I installed GOG Galaxy.

Restart GOG Galaxy and hit the install button. The game should now properly download.

This method worked for me and hopefully it can help some of you as well.

IT doesnt work find a new solution plz