Thanks to KWin 5.25.5, the IMHO most annoying bug on the PinePhone with Plasma Mobile (452967 – kwin_wayland: touch input does not reach GTK or Chromium popup menus (subsurfaces)) is fixed with this update. 
In particular, this also means I can now manage my passwords in (GNOME) Secrets (formerly known as Password Safe). (There was one mandatory popup in the workflow, the choice between “New Entry” and “New Group”, that previously made this unusable under Plasma Mobile.) As long as we do not have a mobile-friendly KWalletManager, Secrets is really the best option for that as far as I can tell.
And, also thanks to this fix, Geary (still the only mobile-friendly e-mail client out there) is now fully functional under Plasma Mobile, e.g., the address autocompletion suggestions can finally be selected, so I no longer have to type the whole e-mail address every time. And I can reply to a mid-thread mail, and lots of other small optional features that require popups.