Ubuntu was pretty good, until 2010 or so. People who still recommend it probably haven’t used it in the last 10 years.

“PPA” is Ubuntu’s branding for third party repositories. So, of course you will have a hard time adding a Ubuntu-specific third-party repository to anything that isn’t the Ubuntu version it’s made for…

Debian of course supports third party repos, just like Ubuntu. On Debian they just aren’t called “PPA”.

For more information on how to add third party repos to Debian (or Ubuntu, if you don’t use Canonical’s weird tooling), check out the Debian Wiki page on UseThirdParty or SourcesList. There’s also an (incomplete) list of third party repositories on the wiki: Unofficial. And just like with PPAs, anyone can host a Debian repo.