Eventually, by making a fresh account, taking checksums of its dotfiles, adding an applet, and taking checksums again, I found out that the new panel configurat

Eventually, by making a fresh account, taking checksums of its dotfiles, adding an applet, and taking checksums again, I found out that the new panel configuration lives in a file called .config/dconf/user that is an opaque binary blob. I think the OP is a perfect candidate for Arch Linux.