I am unable to download the offline installer for Close Combat 3. The installer shows on the Extras page as a file that can be downloaded. But clicking the file doesn't download it and I can't see any other way to enable the download. I've downloaded the manual from the Extras page but this file doesn't seem to actually be there for download. Any ideas about how to enable this download would be appreciated, as I do not always have Internet access on this computer.

Make sure you're clicking the little arrow at the end of the row, not the row itself. The mouse cursor should turn into a pointing hand when you can click to start the download.
This is understandably confusing, since clicking anywhere in the row used to work in previous versions. The row still gains a highlight when the mouse is over it, and it becomes brighter when clicked, giving you the impression it's doing something. I reported this to support on April 12th.

If all else fails, you can download your content using a web browser. Go to your library (user menu at the top of the page - Games). Click a game there. Extras are on the right side, while for Offline Installers you have to click the section with that name to expand it (it's near the bottom, below the big blue download button).

the extras page as in the one in Galaxy app... so you are using Galaxy to download off line installers?

yes = see image "files 1" & "files 2"

the Galaxy app assumes you may want to download files after so clicking the extras "link" makes it goto the "downloads" area where your settings may be set to not download until you goto that area and tell it too... note this default is Gog but you can change it so my point is it may have just goto that que and waited

where you can find the manual = 2 options;
1. click the right hand icon of a folder in the downloads area... its highlighted in the image
2 goto your Galaxy settings area and see where you have it set to send files your download [again see the image] but by default it should be in the game folder in a "downloads" subfolder

you say you don't always have internet... Gog servers have been super patchy this week and if you have very limited download speed it could just be that blocking things