
Samsung Z1
The latest firmware for Samsung Z1 (SM-Z130H) is Z130HDDU0CPI1 with Android 6.0.1, released on September 12, 2016 for 4 regions (CSC). Every official firmware build for SM-Z130H, 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/Z130HDDU0CPI1
SM-Z130H started on Android 2 and has received 2 major Android upgrades; it now runs Android 6.0.1. The newest build, Z130HDDU0CPI1, was released on September 12, 2016. No new build has appeared for 123 months, so regular updates for this model have most likely ended.

SM-Z200M

SM-Z400F

SM-Z400Y

SM-Z300H

SM-Z200Y

SM-Z200F
The newest firmware for SM-Z130H runs Android 6.0.1: build Z130HDDU0CPI1, released on September 12, 2016.
The latest build for SM-Z130H, Z130HDDU0CPI1, was released on September 12, 2016 (10 years ago).
SM-Z130H has had no new firmware for 123 months, so regular updates have most likely ended.
Yes, all firmware files for SM-Z130H are 100% official, original, and obtained directly from Samsung servers.
To flash SM-Z130H, 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-Z130H.