The cleanest upgrade path I could devise with my blunt force devops style after a few failed attempts, was just to full on remove PHP 8.0 and then install 8.1 afterwards. In this case 8.0 was installed via the ppa:ondrej/php prior and there is no good way to do a straight normal upgrade as these PHP packages are annoyingly to me, built to be installed side-by-side.
Pegasus Gate