Once unlocked, you have several options. Based on XDA-Developers forums and Telegram groups dedicated to the Vivo 1801 (codename: pembo or Y83), here are the top stable builds.
Due to the rarity of official guides, this is a high-level overview. Check XDA-Developers or Telegram groups (@VivoY83Updates* typically) for precise files.* vivo 1801 custom rom
Some Vivo 1801 units can flash an engineering build of Funtouch OS that has fastboot oem unlock enabled. These leaks exist on Chinese forums (need login). Once unlocked, you have several options