(lineage-18.1-20210809-nightly-pro1-signed.zip on August 5 security patch installed smoothly using adb sideload and Open_Gapps-arm64-11-pico-20210712)
...But keyboard bug reintroduced is not yet fixed, see comment from @Sean McCreary above.
Did not try to do a factory reset first...
But did try to flash back to 0726, and that claimed the data to be corrupt, so was forced to reset...
So made a third flash WITH a wipe... and that did not work with the 0809, so went back to 0726, with another wipe required. And things work again. I hope for better luck next week . 😇