This is very helpful. Please do so.
In the meantime, looking at the posting history:
@bruceax , can you please check if you have the following installed?
- light-locker
- xflock4
- xscreensaver
- another screensaver app
Light-Locker can interfere and if installed, can be removed.
Using the default xfce screensaver instead of xscreensaver may also be what you need. Please see here:
https://docs.xfce.org/apps/screensaver/start
Under Activate Screensaver on the above page, note the entry for On Screen Keyboard Command. Your command will be
onboard -e