Earlier quoted context omitted.
Gimp? Although the UX feels so outdated. https://github.com/KenneyNL/Adobe-Alternatives#photoshop
If you ever worked professionally with PS, you are getting tired of recommendations of tool that is capable like 20% of PS.
Creating a specification for minimum viable features of a raster editor able to replace Photoshop would be fantastic.
Could serve as a roadmap for alternatives and for bragging rights: "Painter2900: implements 99% of the Rasterflames Liberation Standard, and more!".