Change your code of your theme now.
The new code (see images above) will work with the current leftwm application and with the new one to be released this week-end on 15/01/2021.
But the old code will not work with the new leftwm application and will cause breakage if you do not change it.
Get the new code in when you update your system.
Get the new code from /etc/skel and copy/paste it in your home directory or use the alias skel.
Update your themes
Type “leftwm-theme” in a terminal and learn the codes.
We have made aliases for some of them. Type “alias” in a terminal to see the aliases that start with “lt”.
FIrst uninstall a theme and then re-install it.
That is the only way the new code can come in.
Upgrade command is being developed and is not ready yet.