Now running a mostly-bullseye system, I noticed to my dismay that
xfce4-clipman-plugin (and xfce4-clipman itself) no longer show the most
recent clipboard entries.

Hopefully the attached screenshot demonstrates the issue, the result of
selecting 1 through 20 in a terminal, and taking screenshots (not attached)
after 10 and 15. Maximum items is set to 10 here. Selection sync and history
order reversal are both enabled.

Oh, I was about to hit Send on this report when I found https://gitlab.xfce.org/panel-plugins/xfce4-clipman-plugin/-/issues/33
which is likely the same bug.