I just learned something new, just the other day - like two days ago.
With the current, and previous, version of Lubuntu all you need to do is delete the panel's config. Then, you reboot and it automatically generates the default config for you anew.
So, it works with LXPanel and LXPanelQT (I think that's the name - I don't use 20.04 on a regular basis).
It may just work with Cinnamon. Back up the panel's config folder (or just rename it) and reboot. Maybe it'll reset it as the default. If not, you can just name it back or restore your backup.
I did not know this until just a day or two ago.