@Ambrosia7177 I feel like you are beginning to overthink in your choice of image editor somewhat.
All choices
@OldMacs4Me listed two posts earlier are viable options. PS Elements perhaps not, since its licensing isn't that great.
Krita has a nice artist-friendly GUI, and also offers most of the general editing features that most other image editors have on offer. Krita started life as a general image editor, but the developers decided to focus on digital drawing and painting with animation options instead.
But it still has quite strong image editing options.
@OldMacs4Me The healing brush in Krita is good (if a tad slow).
Is Krita layer-based? Is Affinity Photo layer-based? Is PhotoLine layer-based?
All of them are, as are Acorn8, Pixelmator, Elements, Photoshop, ...
Can anyone speak to how Krita compares to Affinity Pro as far as ease-of-learning, ease-of-use, and overall capabilities for editing photos and creating thumbnails for YouTube?
Affinity Photo is much more focused on general image editing, and the performance of Affinity Photo in this regard is much better. In particular when working with larger files.
I found Affinity Photo to be kinda like a double-edged sword that cuts on both sides. It has a good feature set, with some features better than Photoshop. And other parts I find utterly intolerable and frustrating to work with.
No software is perfect, though, and I approach these tools from a very experienced level. So small papercuts that don't matter to most average users can absolutely kill my workflow.
But again, ANY of these image editors would work well for your needs. That is why you ought to try them all out (they all have trials) and get a feel for them. Everyone is different: I know people who took to Affinity Photo fast, and love it. I also know people who decided to switch from Photoshop to Affinity Photo, then tried PhotoLine, and switched to PhotoLine for their main image editing app (not that many of those, though lol).
PhotoLine is probably not a good fit for you due to the lack of docs and tutorials. Great forum, with direct support from the devs. And needs some customization in the preferences before it handles well. (Personal note: it is incredibly versatile and powerful, though! And I love the core workflow and freedom it offers compares to other image editors, including Photoshop! It also plays incredibly well with other apps via its live app link option.)
Elements is not a good fit for you due to licensing issues.
Acorn8 might be a good fit for you, but again - like PhotoLine - not that popular, and while there are more tutorials online, its community is just much smaller than the likes of Affinity, of course.
Pixelmator new version: Haven't played with that one. Seems more than good enough for your
@Ambrosia7177 's purposes. It's Apple owned now. Not sure if that is a good or bad thing, though. Reasonably popular, and tutorials can be easily found - at least for the older version.
Krita is free, so can't hurt to have it in your toolset. And good general image editing tools. Nice forum. But most tutorials tend to focus on the artistic side, less on general purpose image editing; that is true.
Affinity Photo would be a great fit for you. Tons of tutorials, room to grow. Great forum for quick support. Perpetual license. But the future might bring some changes to its licensing. But that is up in the air for now.
And yes: Preview can deal with some of your requirements as well.
So, we're back to square one! ;-)
@Ambrosia7177 Nothing is set in stone. Change is part of life. Your choice of image editing sofware should be led by what you need NOW and in the near future, rather than worrying over things that might or might not come true in 2, 3, or 10 years down the line.
Anything you learn in any of these image editors is transferrable knowledge and will assist in making the transition to another image editor, if that turns out to be the case in a few years.
As I wrote before in an earlier post: only you can decide, and the best way is to download a few, try them with a small project, and than you'll quickly figure out which one matches your expectations and approach.
I wouldn't be led by anxiety about what-ifs and what-could-bes. Focus on the present and the upcoming months to just get started with any of these options.