For anybody switching from Photoshop to GIMP, there are tons of different resources to help. There are books[1], video courses[2] (especially on Udemy), blogs, and just about anything else you can imagine. GIMP isn't a full replacement, but I do know several people who have made the switch.
I bought "The Book of GIMP: A Complete Guide to Nearly Everything" and I didn't personally like it, but many people do.
And if you need a commercial alternative, for professional shops that need/require it, Affinity Photo is very good. Serif only offers perpetual, per major version licensing (i.e. no subscription) and offers a 'universal' licence if you use multiple platforms (Windows, Mac, iOS).
Yes thanks, that's a great point. I haven't had good luck with Krita personally, but I also haven't put hardly any time into it. I've heard very good things about it so I really need to give it some dedicated time.
They serve different workloads. Other than GIMP Affinity is also a great alternative, not FOSS, but buy it for life with an incredible price that includes feature updates.
I bought "The Book of GIMP: A Complete Guide to Nearly Everything" and I didn't personally like it, but many people do.
[1]: https://www.gimp.org/books/
[2]: https://www.udemy.com/courses/search/?src=ukw&q=gimp