According to posts on Reddit/SonyXperia, some users are having issues with the new firmware update 64.1.A.0.948 flashed onto the Xperia 1 IV.
Screen shot Reddit/SonyXperia
The current firmware version should be 64.1.A.0.941 and the latest problematic firmware is 64.1.A.0.948.
According to this user, he rebooted it at least 7 times and force reboot and it finally worked.
Some have no issues updating to the newer firmware.
A crucial reminder for firmware updates: ensure you maintain a battery level of over 20%, and having even more charge is advisable. Refrain from using any other applications while the firmware update is in progress.
Comment below if you have any issues updating the firmware.