Look up Syncthing and then never stop trying to replace closed source and paid software/services. Like any time you launch something ask yourself “does this hit the same way as when I swapped to Syncthing?” If the answer is no you then put “[name of thing you want to replace] foss alternative” into your search engine of choice. You’ll end up down so many rabbit holes, but you’ll come out the other side a whole lot better at making your technology work for you, not the company that made it, and with a suite of free open sourced tools you are in complete control of.

Here are some tools I use that are super easy to get going.

• Syncthing (cloud storage replacement)
• KeepassXC or Pass if you’re a command line person (locally stored password manager, coupled with Syncthing you have your own private cloud password manager
• Tailscale/wireguard (private VPN that allows you to easily connect all your devices without exposing any of the traffic to The Internet)
• PiHole (a DNS sinkhole that blocks a lot of ads and tracking on your entire network, bonus points if you set it as you Tailscale DNS provider to give all your devices ad block no matter where you are as long as the device was a connected to Tailscale)

Those are the ones that got me going and I personally believe act as a solid core. Most people will find all of those useful. Other services are more user specific, but that’s a lightweight bundle of software that your RPi will handle well. Much more and you might want to look at beefier hardware.

It's a bit newer, but Immich is a very promising Google Photos replacement.

I recommend setting up a NextCloud server.