LineageOS seems to make a name change just now with the boot and recovery thing. For reference, https://topjohnwu.github.io/Magisk/install.html is what I reference. The file you get instructed to path is the boot.img. Note how "you have to do something after every ROM upgrade" does not get mentioned - so it is a little bit better than I thought if Magisk has an action in the app that can be run before the reboot, but that's still way too brittle to be useable.

(I vouched for your comment, it was hidden, that's normal for new accounts.)