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 (OrangeFox Official or TWRP official)
• Backup your internal storage because "Format Data" will wipe everything

Procedure: (OSS vendor based ROMs - all modern AOSP ROMs that are not ports)

• Boot/reboot to recovery (hold Volume Up + Power while booting)
• If the custom ROM you're flashing has a recommended firmware version, flash it. You can find firmware here. If you're currently running the same version of MIUI or if the last firmware version you had flashed is identical, you can also skip this step.
• Flash custom ROM.zip
• Flash GApps + any GApps addons if you flashed the gappless/vanilla build of the ROM (Optional step). Use GApps recommended by the ROM (if none recommended, FlameGapps and NikApps are the most popular choices), for download links refer to the #gapps note.
• 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: (non OSS vendor based ROMs - mostly old AOSP ROMs and ports only)

• Boot/reboot to recovery (hold Volume Up + Power while booting)
• Flash MIUI stock ROM recommended by the ROM. You can find all of them here. Flashing the full ROM is required because it contains both firmware and vendor files. If you're currently running the same version of MIUI or if the last version of MIUI you had flashed is identical, you can skip this step. You can flash the fastboot version of the MIUI stock ROM through Mi Flash Tool or 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). Use GApps recommended by the ROM (if none recommended, FlameGapps and NikApps are the most popular choices), for download links refer to the #gapps note.
• 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 etc.) 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 keep your storage encrypted. If you want to flash a ROM and disable storage encryption, check the #dfe note.