It's 'horses for courses' when it comes to image-manipulation software.
Photoshop is great but it's got a massive learning curve. (I use Photoshop 6, which is ancient but still does all the key stuff).
GIMP (which is free) can do everything that Photoshop can but, again, with a steep learning curve. (I've got GIMP on my computer too). It can actually be quite tricky for experienced Photoshop users to switch to GIMP, as some things need to be handled in a completely different way.
Serif has always offered superb software and, until fairly recently, they offered older editions of many of their programs free of charge. I've used both the free and paid-for stuff that they offer, with PagePlus being my DTP program of choice. I find it slightly annoying that they seem to have merged most of their separate titles (e.g. PhotoPlus, which was a great image-manipulation program) into the Affinity brand but I'm unsurprised that you find it easy to use.
There are still some decent freebies available though. Irfanview, for example, is principally known as an image-viewer but, if you 'look under the bonnet', it's actually a really good image processor as well. (You can use Adobe plug-ins with it, extending its inherent capabilities). If I only need to make a few tweaks to an image it will be Irfanview that I look to first.
Paint.NET also has plenty of fans here on AB.