I do not care much about "look and feel"
It benefits you when an application doesn't do surprising things. Even basic things like clicking in an edit control, it's better for you if that results in the same outcome across all apps (stuff like does it select all text? does it place the caret at the end?).
Even for command line apps, consistency is good (see https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1...). Are options specified with a hyphen? Two hyphens? A slash? Are lists delimited with comma or semi-colon or something else?
Qt4 and Qt5 applications are unsupported, but IgKh/CuteCosmic has a Qt6 Platform Theme that integrates with the cosmic theme system and applies that theming to Qt6 applications. Though it won't work in 24.04 because most of the KDE/Qt apps in this release are based on Qt5, and the version of Qt6 is too old.