We love to praise linux constantly and tell everyone to change to it (they should) but what are your biggest annoyances ?
Mine would be, installing software (made even more complex by flatpaks being added, among the 5 other ways there already were to install software) and probably wifi power management issues.
There are always problems with the global menu widget on Plasma. And recently it has been refusing to work as a single button, instead I have to switch to showing all options as separate buttons which looks terrible with my panel setup.
Also applications making packages that could have easily been optional, required, just because users will think the app has broken functionality otherwise. KDE Plasma handles this best by replacing setting pages in the setting app with a note with instructions and showing normal warnings in other apps.