OK, I'm posting this for all of you who may either install Lineage without doing all the incremental updates (as per directions in the OP), as well as for those of you who may want to opt out of a working Lineage ROM in the future. I'm doing this because I just went through 3 days of Hell just trying to get back to where I was before coming over to Lineage:
If things don't go your way after installation, or if you just want to try a different ROM (or if you just want to rid yourself of Lineage Recovery), do the following:
1) Get the 13A kdz from lg-firmwares.com for your device
2) Get
LGUP_DualMode and run SetDev.bat before running LGUPD.exe. This will allow you to reflash your stock kdz in REFURBISH mode, which is the only method that will get you back to stock. From Download Mode on your V20, flash the 13A kdz with REFURBISH checked.
3) You're still not out of the woods yet because although you are back to the stock ROM, you still cannot flash the boot partition without using the RAW command. Use the
DirtySanta exploit as directed UNTIL YOU COMPLETE STEP 2.
4) EDIT the file called step3.bat. THIS IS CRITICAL or you will be back at reflashing the stock kdz and doing this over. Where you see the 4 lines that say:
fastboot flash boot boot1.img
Change this to add the RAW parameter (all 4 times):
fastboot flash:raw boot boot1.img
If you fail to do this step, you will get the error: Couldn't parse partition size '0x'
5) Run Step3.bat. Once completed, your device will reboot. Reboot to recovery and you should have TWRP. If you have a VS995 (Verizon model) you will probably be stuck at the boot screen indefinitely. Pull your battery and boot into recovery.
6) You will have to mount System and go to the Repair File System option (this may only affect VS995 users but YMMV). Change to ext2, then change back to ext4. For good measure, I also upgraded to the latest TWRP as well.
7) At the Install option, you should see that 0MB error disappear for your Internal Storage and it should now reflect your actual hard drive space.
8) Flash the ROM of your choice. If you're using Lineage 18.1, be sure to start with 15.1 and increment installations as per xxseva44's direction until you get to 18.x.