About open source projects - Is it useful for career?
In short: Yes. A lot of engineers get hired due to their open-source contributions: Back at Meta, we would reach out to external folks contributing to our major libraries to see if they want to work at Meta. Open-source is both good for jobs and building up your skills. However, there's a lot of nuance to this.
Having a meaningful open-source portfolio is hard, especially if you're a more junior engineer. It's not just something you can just pick up and have hiring managers come knocking on your door the next month. The major repos (i.e. the ones you want to work on to get the most attention) have massive, complicated codebases that can take weeks, if not months, to really learn.
I talk about all this more in-depth here: "What technologies or stacks should I create a project to add in my resume for entry level software jobs?"
To be 100% honest, contributing to other folks' open-source is too daunting for me, haha. Just going through the giant READMEs is so scary. This is why I just do side projects instead (and I open-source the code): How To REALLY Level Up Your Coding Ability With Side Projects