I use parcellite. Sensible UI, has all the functionality I need and it's not tied to any desktop environment. The functionality I care about:history, including customizable persistent entriescustomizable key bindingshandles both primary and selection and can sync themcan trim whitespacecan launch customizable actions on the active entry
Selection buffer.Unless you mean clipboard manager, in which case it'll depend on your desktop environment.
In that case gpaste (if you use Gnome). Before that parcellite was my preference, but around the transition to Wayland things broke for me.
CopyQ