Hey, the official documentation is here: https://github.com/keepassxreboot/keepassxc/blob/develop/docs/topics/AutoType.adoc
Essentially, KeepassXC Autotype is fully supported on KDE Plasma 6, and all configuration is done within the app itself. The KDE settings you may be thinking of was in 5, but that is no longer the case when running on 6.0+.
It uses XDG Desktop Portals when run under Wayland; it should all be set up already if Auto-Type is working but essentially you need XDG Desktop Portal and the xdg-desktop-portal-kde package to allow it to integrate with the desktop.
The limitations on wayland are that it can't match to a specific window title and can't track when the keyboard focus changes between windows (due to how wayland works). The overview does note that certain other input methods can conflict with Auto-Type. But other than that it should be working fluidly without issue.
The only other consideration I can think of is are you running KeyPassXC natively or as a flatpak? Flatpak can sometimes be more locked down than needed for some apps. You could install Flatseal and ensure KeePassXC has the right permissions to access services outside of it's sandbox.