I launched Raspberry Pi OS Bookworm lite 32-bit on my 32-bit Raspberry Pi 4 and when I run the command uname -a, I got this output:
Linux raspberrypi 6.1.0-rpi7-rpi-v8 #1 SMP PREEMPT Debian 1:6.1.63-1+rpt1 (2023-11-24) aarch64 GNU/Linux
When I took the same SD card into my Raspberry Pi 3 B+, the result was:
Linux xaris 6.1.0-rpi7-rpi-v7 #1 SMP Raspbian 1:6.1.63-1+rpt1 (2023-11-24) armv7l GNU/Linux
When I launched Raspberry Pi OS Bullseye lite 32-bit on my Raspberry Pi 4 (same as in the first case), the result was:
Linux xaris 5.15.32-v7l+ #1538 SMP Thu Mar 31 19:39:41 BST 2022 armv7l GNU/Linux
Why, in the first case (rpi4; 32 bit bookworm), does the OS think that it is a 64-bit system?