SD card slot not usable when booting from USB?

I had the idea to store some media on a spare SD card. My RPi 4b boots from USB. But when I put in the card (128GB SDXC) it is not recognized. I even tried with a 4GB card, which is also not detected.
Is the SD slot deactivated when the RPi boots via USB?

I found the culprit.
In /boot/config.txt I had SD card hotplug disabled (dtparam=sd_poll_once). I just commented this line and rebooted and now it’s working.

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yes, we do this to reduce overall CPU load. The constant SD card pull is increasing it a bit.