
Samsung Galaxy S Ⅱ
The latest firmware for Samsung Galaxy S Ⅱ (GT-I9100P) is I9100PXXLSU with Jelly(Android Bean), released on July 25, 2013 for 3 regions (CSC). Every official firmware build for GT-I9100P, 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/I9100PXXLSU
All 5 builds in our database run Android 4.1.2 (Jelly Bean). The newest build, I9100PXXLSU, was released on July 25, 2013. No new build has appeared for 161 months, so regular updates for this model have most likely ended.
Box codes of GT-I9100P for different colors and markets. Firmware is chosen by the model code GT-I9100P and your region (CSC), not by the SKU.

GT-I9308

GT-I9268

GT-I9228

GT-I9210

GT-I9108
The newest firmware for GT-I9100P runs Android 4.1.2 (Jelly Bean): build I9100PXXLSU, released on July 25, 2013.
The latest build for GT-I9100P, I9100PXXLSU, was released on July 25, 2013 (13 years ago).
GT-I9100P has had no new firmware for 161 months, so regular updates have most likely ended.
Yes, all firmware files for GT-I9100P are 100% official, original, and obtained directly from Samsung servers.
To flash GT-I9100P, 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 GT-I9100P.