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.
AFAIK Knox would trip a fuse if you installed custom firmware and would prevent you from using banking apps and the like permanently but you were still able to flash the firmware.
I definitely remember the bit about the fuse. I can’t recall if you could flash the firmware or not. You might be right about that. I never owned an S4. I went to HTC after my S3. I regret that. Pretty phone, but what a clustertruck inside.