This app interrupts usage of the target app by setting up an automation (in the native Shortcuts app) that triggers when the target app is launched.[1] This means you can skip the app entirely and try to set up your own poor man's version. I fiddled around a bit and it's possible to set up an automation that automatically exits back to the home screen after some pause, or displays a notification to try to nudge you out of the app. This is not as good as the app but it is free. Also, without the Safari extension, I don't think websites can be blocked.

My own strategy is to simply use pi-hole to block time-wasting websites entirely. It's kind of a sledgehammer, but it works for me.

1: https://tutorials.one-sec.app/setup-ios