According to tipster Ice Universe, Samsung has disabled Odin, a proprietary firmware flashing tool typically used to install stock firmware, install custom ROMs, and restore devices. It also appears that Samsung has removed “Download Mode,” which acts as a gateway for Odin. This change appears to have been made in the latest One UI 8.5 firmware and currently affects the Galaxy Z Fold 7 and recently launched Galaxy S26 series.
i remember many years ago i flashed, i think it was Lineage OS maybe android 8 or 7? on galaxy s2. There were something like 10 android versions ahead of last official relase.
I checked xda, and theres lineage os 19.1 (android 12) available for galaxy s2.