Personally, I use both Adobe Photoshop & Adobe XD, but I mainly prefer Adobe XD for UI Design, it’s really simple & easy to use, I highly recommend Adobe XD if you’re new to UI Design!
Photoshop is always the go-to, although there are some decent free alternatives.
I like Pixlr E its my goto source
Affinity Photo is probably one of the best competetors to Photoshop imo.
It costs just £50 and often goes on sale for half price.
I use it as my main photo-editing software and I can honestly say it’s pretty dang good.
I’ve used photoshop before and Affinity doesn’t miss much when compared to it.
Definitely worth a look!
You can also use blender but it will take a while to learn
I use a combination of Photopea and Figma.