Experiences Finding and Working with Nonprofits?

I have a strong need for the work I do to be meaningful. The strongest contributor to that is that it "helps people", especially people who don't have a lot of money. I have to really believe what I'm making is "good", from a moral perspective. If I'm working for free, it feels even better. Ideally I'd work for free all the time. (My favorite thing to do is give people money, but I can't find a way to do it full-time ;)

FreeCodeCamp used to have a thing where at the end of the course you'd be paired up with a nonprofit and spend a few months working with them.

That always sounded great to me, so I was sad they stopped it and wondering if there are any sites like that, where you help nonprofits for free.

I actually found many such sites with a web search, so I was wondering if any of you have experience with such platforms, and more broadly advice about (and experiences with) working with nonprofits in general, if there any significant differences there to keep in mind.

Worth mentioning that I strongly prefer freelancing, in case that matters.

Thanks!