Custom ROMs:
PixelExpirence
https://forum.xda-developers.com/realme-x/development/rom-pixel-experience-plus-edition-t4066879
RevengeOS
https://forum.xda-developers.com/realme-x/development/11-revengeos-4-0-r-realme-x-t4165129
EvolutionX
https://forum.xda-developers.com/realme-x/development/rom-t4044901
Mokee
https://download.mokeedev.com/rmx1901.html
Official
https://www.realme.com/cn/support/software-update
Flash Steps:
1. unlock
https://c.realme.com/in/post-details/1247421596461694976
2. flash TWRP recovery
2.1 volume down + power enter fastboot mode
2.2 fastboot flashing unlock
2.3 fastboot flash recovery twrp-3.4.0-0-RMX1901-mauronofrio.img
2.4 fastboot reboot recovery
2.5 flash the OF_avb_patcher_mauronofrio.zip inside TWRP for preventing TWRP lost.
3. flash roms with TWRP
important: click Wipe Data button to clean data, or you will boot into recovery instead of system.