Did you used the arrow keys to highlight the selection ? This is the important thing to see the "Mark as owned" button, you can't see that button using only the mouse.
Yes, I have. Did you try adding a "Other" game entry to an already owned game through another integration like GOG or Epic? Could you show a screenshot?
I did this with Minit
, which is a game that I have through Epic as a free giveaway and itch.io as part of a charity bundle. If run through Galaxy, the epic version launches the epic launcher to launch the game. The itch version just runs. Where you have Install, I had a Mark as Owned option.
You get this because you probably have an itch.io integration. Could you try adding a "Other" game entry through this means? With screenshots at best.
If you change it from "Epic" to "Other" then the install button will be replaced by a play button.
You can't change it, if you don't already own the game as "Other". You can't see the diamond if you haven't marked it beforehand (or own it through another shop). Which you can't if you already own the game elsewhere. Unless you can show me with a screenshot.
Unless there're different versions of Galaxy, all these solutions don't help the problem if you own a game already and haven't marked it as "Other" beforehand.
After all these 2 years since all GOG essentially did was adding Epic to Galaxy. I'm not convinced there's much in the making anyway. So I jumped ship to Playnite (https://playnite.link
/) which does a way better job at adding new games, updating metadata, grouping duplicate versions (through an addon) and much more. The integrations also work for more than a week without crashing.