Built-in Updater offers the 18. But it is not allowing update.
I did the following:
* Update Magisk to recent 22 out of magisk app.
* Downloaded latest TWRP image.
* Patched it by Magisk
* flashed the patched TWRP with:
dd if=/sdcard/Download/magisk_patched_twrp.img of=/dev/block/bootdevice/by-name/recovery
So I do have latest TWRP and Magisk which seems to me a perfect starting point.
* downloaded latest LOS, boot into revovery and flash by sideload
"adb sideload linage-18.1.xxx.zip"
* wipe cache and dalvik
Bad luck, I just to come to that LOS install logo. And I thought I did all right....