Lots of possibilities. Why are you still using 18.1 when it was discontinued? You should use 19.1. You are probably using the gapps meant for 19.1 (android 12.1) but you are installing android 11(.1) . I don't use magisk, but you may be screwing up versions there too. Lastly, you maybe didn't copy partitions from A to B as you were told to do so in instructions. Those are all potentially your fault, or even a combination of multiple faults. Or maybe none of them are. But that's the best I can speculate. 99% of the time people have problems, they skipped something important without realizing it or mismatched gapps and android versions. Which gapps are you using?
If it were me, I'd try to just install LOS without any extras first, since you already reset anyway. If I then was able to continue, I would try it again with Gapps ( I prefer NikGapps core btw ). If I succeeded a second time, then I would try to include Magisk as well. You have to start eliminating variables to isolate the problem.