FreshRSS, as I said, is an RSS client as a server, but it's also so much more! I haven't explored too deeply, but it can scrape websites that don't support RSS!
If that's not enough, it takes the load off your phone, which doesn't sound like much, but think about it. Once you get >=100 feeds, your phone would be querying >= 100 rss feeds every 10 minutes or so depending on your settings. Whereas when it's your server doing it there's no need to worry, as your phone's just querying one website (the server).
By the way, it's not just for blogs! Recipe sites, news sites, comic sites (XKCD), and lots more use RSS too! No matter who you are, RSS can probably help you out in some way. Personally, I've used it to shirk my social media addiction. Now, instead of constantly scrolling Reddit, I'm constantly scrolling my RSS feeds. It's not as good as doing useful things with my time, but I'm getting there!
If you're interested, check out blogroll for a great big list of blogs about all sorts of things.
Pro Tip: You can subscribe to substacks by adding "/feed" onto their base url.