My next question is more complicated because the FE ecosystem is expectedly even more crazy than in BE.
My goal is to invest some time in learning the basics of front-end so that I know enough to both build a traditional server rendered app and a modern SPA.
With so many choices, I have a feeling that React is by the very definition that boring technology and a pretty safe choice. In my case, employment doesn't matter though since I don't need to be hired as a FE developer so I can just learn the nicest one.
Svelte seems to be a pretty popular choice, but I have heard that the changes are still pretty major so not sure whether it makes sense to give it a serious try.
What library/framework would you choose and why?
Once you have a firm grasp of the DOM and browser quirks and have figured out how to write an efficient {insert simple/intermediate component here}, move on to custom HTML components using LitHTML or Svelte or some such. Once you grok what's going on there, you're ready for any framework you want :)