ALPS vendor custom ROM Installation steps:
1) Download ROM
2) Reboot to recovery mode (TWRP)
3) do a "Format data" in wipe menu and type "yes"
4) do wipe in wipe menu > advanced wipe. check all the checkboxes except for external sd, usb-otg.
5) Flash alps vendor
6) Flash ROM that support/only for alps vendor
7) Flash gapps (For opengapps i recommend use pico variant)
8) Flash Magisk (v23 recommended)
9) Flash fixes that needed in the rom (like sound on call fix mostly)
10) Reboot system

Note:
- For 'arm alps vendor' use the file that is for "arm" (most arm roms codenamed only "certus")
- For 'arm64 alps vendor' use the file that is for "arm64" or roms with "certus64" codename.
- For nomagisk you need to get boot.img from vendor zip and flash it after flashing rom
- If your from oreo, upgrade to miui pie first ! (10.4.1.0 - 11.0.8.0 )
- A64 != Arm64 (a64 is Arm32 binder64 not Arm64)