I was on 17.1 with magisk. yesterday I followed the instructions in the wiki (sideload lineage 18.1 and mindthegapps), and have a fully working upgraded phone. done with the april 17th build.Still trying to get a handle on this upgrade.
The original build of 18.1 seemed to have people successfully dirty upgrading from 17.1 to 18.1.
My reading of this thread is this no longer seems to be working on the latest build for people?