1Blocker just released an update as well, live in the App Store now, stating in the change log that they are supporting Safari Web Extensions through what they are calling « 1Blocker Scripts ».
Can confirm on iPadOS 15, there is now a « JS » and the Extensions icons showing up in the address bar.
The only hassle, you need to go the Settings > Safari and manually allow it everywhere, otherwise you will get a pop up asking you to Allow it or not (for a specific website or wildcard).