I think they are just referring to the Ubuntu pro ads.
This is not spam. If you have random outdated packages from the universe repo on your system it will tell you that they would ALSO offer support for those if you get Ubuntu pro.
Maybe too often, idk. But Linux Mint will “fix” this by also running these old maybe insecure packages but not even offering security fixes.
People need to step down their weird Linux-entitlement horses, and get that Free Software is not free as in free beer.