Installation process for vanilla builds

Steps -

•  Backup all your data (If your data is important to you)
• Format data (goto format data and type yes)
• Flash the ROM
• Boot into the system
• Reboot back into the recovery and flash GApps ( I prefer Open GApps ) or GApps and magisk if you prefer
• Reboot to system
• Now, sometimes Android setup force closes, and sometimes it doesn't, if it does force close just goto Setting > apps and notifications > see all apps > then 3 dot menu > show system apps > search for Android Setup and disable it.

WHY IN THE WORLD THIS HAPPENS?

In my observation, all devices with "Dynamic Partition" have this issue, read more about dynamic partition HERE. I have also noticed that non Lineage or Lineage based ROMs sometimes just doesn't boot, maybe this has something to do with the Lineage Setup wizard.. Also, the Android Setup doesn't force close on Lineage or Lineage Based ROMs.

IS IT RELATED TO YOUR VENDOR? IT DOESN'T HAPPEN ON XXX GUY'S BUILD..

NO, vendor has nothing to do with it. As I said above Lineage and Lineage Based ROMs are unaffected.

WHAT CAN I DO, I DIDN'T READ THIS BEFORE AND NOW I AM HAVING FORCE CLOSES

Simple, format data and clean flash the ROM following the above guide. Or just ROMs with in-built GApps.