I would do other way.
First, boot system from SDcard (without NVME), set it up and have a proper booting device.
Then, connect NVMe, use SD Card Copier (https://forums.raspberrypi.com/viewtopic.php?t=234411) and copy from SD to NVMe. Shutdown, remove sdcard and boot.
For config, try:
dtparam=pciex1
dtparam=pciex1_gen=2
I had some issues with stability on gen3 - long wire paths were not great for such speeds.
Above approach worked for me (and still works). With bootable SD cards allows me to boot Kali (SD) and Trixie (NVMe).