The build packaged in the Ubuntu PPA has at least two striking differences from the official AppImage.
First, the tray icon is formed by a simple checkmark overlaying a circle, instead of by the product logo, the three conjoined circles.
Second, the tray icon produces a simple menu, instead of the advanced popup.
I am wondering why the PPA build lacks the generally more desirable features.
I realize the PPA is maintained independently, but rather than contacting the maintainer directly, I decided it would be more valuable first to seek an answer publicly.
The official AppImages contains all required dependent packages, while the PPA packages only contain the Nextcloud code itself and rely on the system’s versions of dependent packages (e.g. Qt). So for the PPA version, there can be different Qt versions that behave differently. You can find a few remarks depending on your distribution here:
Advantage of the PPA version, since the system packages are used, there is less overhead.
For your case, I don’t know if that is something that can be fixed, I’d report the specific case in the bug tracker. Also, a newer distribution version might help so there is less difference in the versions, e.g. ubuntu 26.04 instead of 24.04.
The icon design would seem unlikely to be bound to the versions of the library dependencies, since any image design could be provided in an appropriate image format.
Outdated library versions explain the more basic popup design much more naturally. Ideally, the dependencies selected by the application package would be compatible versions, but of course, distribution repositories often lag considerably behind the most recent releases of upstream projects.
Curiously, the fancy popup has been featured in earlier releases from the same PPA. The plain popup is actually a recent regression.