Why kernel.pid_max = 4194304 on my system?

Because you are on a 64 bit system and using a more recent kernel. The sentence could use more elatboration.

r9:/home/coop>ps 
    PID TTY          TIME CMD
  54249 pts/2    00:00:00 bash
  80648 pts/2    00:00:00 ps
r9:/home/coop>cat /proc/sys/kernel/pid_max 
4194304
r9:/home/coop>

Note that 4194304=4*1024*1024, or 2^24 I don't know the historical specifics that made it this many bits.

I'm currently running on OpenSUSE Tumbleweed with kernel 6.3.7-1-default (as per uname -a) on a 64-bit machine, but I still see the specified 32768 max_pid. Is the bit architecture relevant to this or perhaps the distribution maintainers are responsible for keeping this variable at a lower value?

Thank you for clarifying that!