
Samsung Galaxy A51
Every official firmware build for SM-A515X, newest first: one row per build with all regions (CSC) that received it.
Specifications of SM-A515, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-A515W

SM-A5100X

SM-A516V

SM-A526N

SM-A520X
You can find the firmware on the model: SM-A515X page.
Yes, all firmware files for SM-A515X are 100% official, original, and obtained directly from Samsung servers.
To flash SM-A515X, you need to download the appropriate firmware, put your device into Download Mode, and use the Odin tool to load the BL, AP, CP, and CSC files.
Downgrading is only possible if the bootloader version (binary bit) of the old firmware matches the current one. Always check the binary version before flashing SM-A515X.