Yeah Trebuchet has that feature.Hello there! I don't have OnePlus 8T, I own Pocophone F1, however it runs offical LineageOS too, and app locker is there! But it's kind of hidden. Long press on the blank space on the home screen, then choose Home screen setting -> Hidden and Protected Apps. And voila! You can choose if you want to block or hide the app from app drawer. Let me know if you found it!
Im using Nova though.
But I found an application that suited my needs here: https://play.google.com/store/apps/details?id=com.sp.protector.free