Looks like mc can no longer enter tar.gz archives on 5.2.0.17, this workaround seems to work:
devel-su cp -a /etc/mc/mc.ext.ini /etc/mc/mc.ext.ini.bak
devel-su sed '/Regex=/s/\\/\\\\/g' -i /etc/mc/mc.ext.ini
That was with gnu sed, no idea if busybox sed works (‘pkcon remove busybox-symlinks-sed’ to get real sed). Found here: [SOLVED] mc stopped to enter compressed tars / Applications & Desktop Environments / Arch Linux Forums it’s supposedly linked to glib2 issue, but ours is much newer than reported there and still happens, so no idea, maybe another regression, but the workaround works