Hello, did you also posted the thread in the Radxa forum? If so, in case you didn't noticed that, I just copy the reply here and hope that could help.
https://forum.radxa.com/t/rock-5c-pentahat-and-emmc/24624
In short words, the emmc worked fine with nvme on ubuntu-rockchip.
After I switch from debian based Radxa OS to ubuntu-rockchip (https://github.com/Joshua-Riek/ubuntu-rockchip/releases/tag/v2.4.0), the problem is solved. Now the OS boot from emmc could use the nvme ssd connected on pcie slot.
I have tested with both 22.04 and 24.04 on Rock 5C and both of them worked fine with pcie connected nvme ssd. The corresponding kernel versions are 5.10.0-1012-rockchip and 6.1.0-1025-rockchip.
There might be some overlay issue and the case was not triggered when booting from SD card.
If you want to dig into this, then I think this thread could be discussing something similiar:
The output of the lsblk, nvme is detected and worked fine.
