Also responded on the jira ticket:
Does selecting the home folder in the file save dialog before saving fix the issue? That would give us a check of if it is the issue from the investigation below is it. (Also it would serve as a workaround for now).
Doing some investigation:
This may be the same file pathing issue filed in signal’s desktop app: Unable to save media or files via Desktop on Linux, while Android works fine · Issue #6912 · signalapp/Signal-Desktop · GitHub
They fixed in Fix file save dialog default path for Linux KDE · signalapp/Signal-Desktop@520620f · GitHub
Seeing mentions of a KDE Portal xdg-desktop-portal-kde issue happening which may be the root cause of the bug. [Bug]: GNU/Linux/Fedora/KDE: file selection dialog doesn't work · Issue #42250 · electron/electron · GitHub
Which means our file selector returns nothing so we just are closing the file selection.
As a fix we can try explicitly adding the home path for these environments, similar to the signal fix.