> Like is it supposed to be this hard to build a UI?
Yes. It is hard to build UIs that are accessible, intuitive, and robust to a wide range of user inputs, interactions, and devices. It's a different kind of hard from backend / infra work.
I agree with what many others are saying here - to get started, you can strip away the complications of React, state management, CSS libraries and just learn basics. Tinker around in CodePen. Create a minimal HTML / CSS / JS static page and serve it with e.g. `python3 -m http.server` or `npm install -g http-server; http-server .` Read through e.g. MDN docs [1].
Find someone - maybe a coworker, maybe a friend, whoever - that knows frontend development better than you do. Pair, ask questions, get some peer mentorship. Ask them to review your frontend code - maybe at work, or maybe throw a Github repo up with a personal project and send them a link.
Find examples of good UI / UX, the kind you appreciate. Pick a small part: maybe it's a specific form field, or an animation, or a data visualisation, or even just a layout. Try to build a simple version of it yourself. Start small, start simple. Even if you don't build the beautiful version, now you might see what small details are lurking in that beautiful version.
Don't forget: you've been a (mostly) backend engineer for ~10 years. How long did it take you to really grok the beauty and challenges there? It will take time and effort. It will also pay off: you'll gain a clearer understanding of what others around you are doing, and how your work fits together with theirs.
[1] https://developer.mozilla.org/en-US/docs/Learn