i am pretty confused, is
this step necessary:
cause
here AVB is not mentioned, what is correct?
Those instructions are pretty generic. Why don't you just follow the OP's instructions...
Installation:
1. fastboot boot twrp.img
2. go to Advanced > Flash Current TWRP
3. after that is done, if you were using a custom kernel, reflash it now
4. if you were using magisk, reflash it now
Updating to a newer build:
1. download new build to internal storage
2. go to Advanced > Install Recovery Ramdisk
3. select the new image
4. after that is done, if you were using a custom kernel, reflash it now
5. if you were using magisk, reflash it now