Poco X3 Pro - Guide for flashing custom ROMs

Before you continue, make sure you follow my EFS + persist backup guide

Requirements:

• Unlock bootloader (follow #unlockbl note)
• Flash a custom recovery (TWRP by Nebrassy is currently recommended)
• Backup your internal storage because "Format Data" will wipe everything

Procedure: (non OSS vendor based ROMs)

• Boot/reboot to recovery (hold Volume Up + Power while booting)
• Flash recommended MIUI stock ROM. You can find them here. Flashing the full ROM is required because it contains both firmware and vendor files. If you're already on it or if you had flashed the same MIUI ROM before, you can skip this step. You can flash the fastboot version of the MIUI stock ROM through Mi Flash tool / Fastboot too but the procedure is slower.
• Flash custom ROM.zip
• Flash GApps + any GApps addons if you flashed the gappless/vanilla build of the ROM (Optional step)
• Flash Magisk (Optional step, only if you want root)
• Format Data > type "yes" and press enter (different from the "wipe data" option)
• Reboot to system

Procedure: (OSS vendor based ROMs)

• Boot/reboot to recovery (hold Volume Up + Power while booting)
• Flash recommended MIUI firmware. You can find them here. If you're already on the corresponding MIUI ROM version or had flashed the same firmware before in the past, you can skip this step.
• Flash custom ROM.zip
• Flash GApps + any GApps addons if you flashed the gappless/vanilla build of the ROM (Optional step)
• Flash Magisk (Optional step, only if you want root)
• Format Data > type "yes" and press enter (different from the "wipe data" option)
• Reboot to system

Notes:

• If you want to flash a custom MIUI ROM (Xiaomi.eu, MiuiMix, Hellas-XTRV) you don't need to flash a stock MIUI ROM or firmware first.
• If you want to flash an update of the ROM you're currently using, you can dirty flash. No need to format data or wipe anything unless the developer of the ROM suggests so.
• Make sure to follow any specific ROM's flash instructions.
• You can't dirty flash a non-OSS ROM over an OSS ROM.
• The instructions in this guide will help you flash a rom and be Encrypted. If you want to flash a ROM and stay Decrypted, check the #dfe note.