If you cannot unlock your bootloader, you can use a "Virtual ROM" app like . This creates a rooted Android environment inside your existing Funtouch OS.

: You can find GSI versions of Evolution X , LineageOS , and crDroid. Prerequisite : You must successfully unlock the bootloader , which is the primary hurdle for most 2. Virtual Custom ROMs (Non-Root Method)

: Consumes more system resources (RAM/Battery) since two operating systems are running simultaneously. 3. Unofficial TWRP & Rooting vivo Y71 - Full phone specifications - GSMArena.com

Because official device-specific builds (like LineageOS or Pixel Experience) are rare for this specific model, you should explore these three main avenues: