How to learn frontend as a newbie?

Should I spend some time watching lessons or tutorials or try and hack together a small side project or should I just learn as I go?

I highly recommend doing the latter. I've literally never gone through a full Android tutorial in my life (and back when I started Android dev in 2013, the tutorial landscape was far worse so this was largely by necessity).

Here's another great thread about this: "Front End Engineering"

A lot of modern frontend technologies were created because they addressed problems with libraries in the past or because browsers weren't able to handle a use case in a simple way.

For example, it might be hard to understand why people use React unless you've had to add/remove DOM elements using Jquery before. Or, it might be hard to understand why you would use Next.js unless you've tried to render React components on the server before.

You probably could jump into the code immediately, and you'd probably be successful in fixing smaller bugs, but you'd be taking a lot of guesses about how everything is working together.

I would dedicate 1-2 hours reading about React, Next.js, and Tailwind so you can get a sense of what they added to the web ecosystem, and how they work at a fundamental level. This might be reading 10-20% of each of their documentation. I would avoid reading 100% of their docs because a lot of it won't be relevant. You can always go back to read the rest of the docs as you come across specific issues with your particular codebase.