Still on the road, but I updated as a dirty flash using the method @FlyingAntero gave for the Pro1 HERE. I also flashed (using the flash-as-a-zip method because all I care about is SU) Magisk 27. All is good. Update was successful, and I have root.
So I now have the Feb 15th nightly. What is curious is that the Feb 19 update, mentioned above, doesn't sow up either on the Lineage download page or the updater on my Pro1x, however, while on Lineage 20, days ago, I did get a notification of the Feb 19 update to Lineage 21.1. Did they withdraw it for some reason?
Whatever the case, M