Hi Andrey,
this is likely a duplicate of #1073959 [1]: long story short, we [2] broke this for
non-Plasma Mobian systems, then fixed it in January this year [3], that was released
with mobile-tweaks_8 which reached trixie middle February [4].
Could you please check whether this issue still happens on a clean trixie install?
Nheko is expected to look different on Plasma (where the style is set in [5]) and
not-Plasma environments, but it should at least work and be usable.
Thank you
marco
[1]https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1073959
[2]https://salsa.debian.org/DebianOnMobile-team/mobile-tweaks/-/merge_requests/12
[3]https://salsa.debian.org/DebianOnMobile-team/mobile-tweaks/-/merge_requests/22
[4]https://tracker.debian.org/news/1616698/mobile-tweaks-8-migrated-to-testing/
[5]https://invent.kde.org/plasma/plasma-mobile/-/blob/master/bin/startplasmamobile.in?ref_type=heads#L13