It’s interesting, as I saw this just in the other topic: Network state filling up terminal
The default is, or should be, that only severity “err” or higher is printed to console, like with dmesg -n 4.
… checked again, indeed the default is to show everything up to info level and up wo warning is only the default with quiet flag in /boot/cmdline.txt.
Can you try this:
echo 'kernel.printk = 5 4 1 7' > /etc/sysctl.d/99-printk.conf
This leaves full boot-time verbosity (all but debug), but reduces regular console prints to warnings and worse. I hope this covers everything from login prompt on.