> But, I want to build beautiful web applications, but I don't get CSS. Like is it supposed to be this hard to build a UI?

IMO, CSS is the hardest part of FE dev. It's deceptively easy, but you can still create good looking UI if you use 3rd party libs like bootstrap, tailwind, bulma etc.

> Recently, I've been trying to learn more about Frontend and started exploring a React project at work.

> Given my experience with this archaic pattern, I've now started exploring HTMX with Golang. This seems more my speed.

Do you want to build FE apps or learn about how FE frameworks? If you just want to build, you can use Golang templates with the above mentioned CSS libs. If you want to learn for career change (BE->FE), you'd have to learn React/Vue/Svelte etc.