Is it possible to play this game on Windows 10? The game starts and plays fine, but I can't save it. I think this game is too long to finish in 1 play. Is there anything that can be done?

I found this in MaG's walkthrough here at Gameboomers.

To save or load a game, 1) either use the F2 (save) or F3 (load) keys or 2) open the diary in toolbar or by pressing F1 and then selecting the various options.

GOG has The Longest Journey and on their download page Windows 10 is not listed as a supported operating system. That doesn't necessarily mean, though, that you can't get it to work.

Doing an online search about this issue, I see some people with Windows 10 saying the game runs and others saying they got the game running satisfactorily but that some tweaking was involved. I also found one Steam forum discussion about this. Most people suggest running the game in compatibility mode, choosing Windows XP.