
Samsung Galaxy S5 Neo
The latest firmware for Samsung Galaxy S5 Neo (SM-G903M) is G903MUBS1BSB1 with Android 6.0.1 (Marshmallow), released on February 3, 2019 for 8 regions (CSC). Every official firmware build for SM-G903M, newest first: one row per build with all regions (CSC) that received it.
SM-G903M started on Android 5 and has received 1 major Android upgrade; it now runs Android 6.0.1 (Marshmallow). The newest build, G903MUBS1BSB1, was released on February 3, 2019. No new build has appeared for 94 months, so regular updates for this model have most likely ended.
Specifications of SM-G903, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-G935TZK

SM-G930AZK

SM-G935AZS

SM-G935TZS

SM-G935AZK

SM-G935TZD

SM-G975WC

SM-G975FC
The newest firmware for SM-G903M runs Android 6.0.1 (Marshmallow): build G903MUBS1BSB1, released on February 3, 2019.
The latest build for SM-G903M, G903MUBS1BSB1, was released on February 3, 2019 (7 years ago).
SM-G903M has had no new firmware for 94 months, so regular updates have most likely ended.
Yes, all firmware files for SM-G903M are 100% official, original, and obtained directly from Samsung servers.
To flash SM-G903M, 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-G903M.