I am extremely hard on my art. I tend to compare my own artwork to those of actual professionals and super popular digital artists, which can become super demoralizing. On the other hand, with a more optimistic mindset it can also be super inspiring.
What I've learned to do instead of just comparing my art to others and putting myself down is yes, compare, but analyze the differences - pick out the small things, make a note of them, and keep them in mind the next time I draw. I'm still being critical, but in a more productive way if that makes sense.
The most important thing, I think, is to focus on how far you've come. Sure, it might feel like your progress is stagnant, but I doubt it actually is. Sometimes when I feel like my art is at a standstill, I put some of my newer art next to stuff I drew years (or even months) ago, and seeing them side by side really shows how much I've improved. It's not much, but it helps a lot.