You could try creating a new user backing up the cinnamon configuration of that new user than restoring that configuration to your user. Why would you want another method if it works using gsettings reset-recursively org.cinnamon?
that worked for me. it was very odd, I have found CInnamon on Fedora 34 to be really solid. then today for no reason, after suspending on leaving work and resuming at home, all the panels had disappeared!
I suspect this was caused by my relatively recent adding of the Spice manager applet and installing a few applets.
in this case, rebooting (which I needed to do after a dnf update) didn't solve the problem, so a factory reset to the defaults was needed.
thanks for the suggestion, had I not found this reset to defaults, I was going to poke around in the .config directory. I think I had to do that in the past when this happened before, so this was much easier.