That said, Corel added a kind of adware to PSP, where it will display promotions for upgrades to the new version of Paint Shop Pro even when you're not using the program. I really wish there was an easy way to disable it, but I'm sure their metrics show it is effective. Parallels are already doing a version of that (but only when you launch the program), and now even Apple itself is using notifications to advertise products & distribute discounts [1]. There's probably no avoiding it now.
[1] https://9to5mac.com/2018/12/18/apple-push-notifications-comp...
It sounds like it's gotten a little worse.
From memory, v9 isn't compatible with Windows 10 (the installer won't work properly), so don't feel you're missing anything.
Serif's Affinity Photo is giving PSP real competition, but Affinity is still quite buggy in some ways on Windows. I'd probably recommend Corel PSP 2018 / 2019 over Affinity for the moment. Paint.NET is great too.
It's a shame that so many tried to re-bundle Paint.net in sleazy ways... though the ads on their own site are horrible, and I don't fault the main dev(s). I just would love to see Pinta or anything else become as easy to use. I may try to dig up PSP7 and see if I can find a key for it.