I tested with the 6.1 kernel from testing.
hbarta@boson:~$ uname -a
Linux boson 6.1.0-0-arm64 #1 SMP Debian 6.1~rc7-1~exp1 (2022-12-01) aarch64 GNU/Linux
hbarta@boson:~$
The problem seems to be worse. It manifests with every cold boot (4 tries.) I was only able to test one warm boot immediately following installation of 6.1 (and shutting down 6.0) and the issue manifested then also. I was unable to further test warm boot because the system never completed shutdown even after waiting 10 minutes. Inserting an SD card got the following message (from dmesg)
[ 46.858495] mmc1: new high speed SDIO card at address 0001
That message was followed by a single block from the timeout message referencing mmc1 and which seemed not to be repeated. The /dev/ entry for the SD card was never created.
Update: While composing this message it did complete a shutdown and reboot. Unfortunately the SD card was (sort of) bootable and the system tried to boot from it and hung, forcing a power cycle and cold boot. On this subsequent cold boot the timeout did not manifest. A subsequent warm boot also did not manifest. The third warm boot did manifest the timeout.
best,