
Samsung Galaxy S4 Zoom
The latest firmware for Samsung Galaxy S4 Zoom (SM-C105S) is C105SKSUANC2 with Jelly(Android Bean), released on April 9, 2014 for 1 region (CSC). Every official firmware build for SM-C105S, newest first: one row per build with all regions (CSC) that received it.
Each firmware build has its own page at https://samfirm.shop/build/{PDA}, where {PDA} is the build number from the list above. Example: https://samfirm.shop/build/C105SKSUANC2
The newest build, C105SKSUANC2, was released on April 9, 2014. No new build has appeared for 152 months, so regular updates for this model have most likely ended.
Specifications of SM-C105, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-C105A

SM-C101

SM-C115W

SM-C1116

SM-C500X
The latest build for SM-C105S, C105SKSUANC2, was released on April 9, 2014 (12 years ago).
SM-C105S has had no new firmware for 152 months, so regular updates have most likely ended.
Yes, all firmware files for SM-C105S are 100% official, original, and obtained directly from Samsung servers.
To flash SM-C105S, 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-C105S.