I used AltStore for a while, but it’s kind of a mess. The project is not super well maintained, it’s buggy, it doesn’t recognize paid developer certificates if your paid account is linked to a business, it requires a Mail.app plugin to run, etc.
There is a community developed fork now called sidestore, which seems to work much better in my limited experience trying it out.
It still requires a bit of setup and you have to set up a VPN client on your device in order to install an app, but it seems more reliable to me.
I’m hopeful that Apple will allow sideloading apps directly in iOS 17 to comply with new EU regulations, but I guess we will see.