I believe that the Proxmox VE installer usually does not allow installing on SD cards. Is this ZFS pool named rpool? Maybe it was installed this way and later the boot drive was changed?
You could remove the drive, wipe it, re-insert it and follow the "Changing a failed bootable device"?
You cannot remove it (in ZFS terms) and I don't know if you can detach it (in ZFS terms). You can probably leave it in. Maybe just re-partition and ZFS will report it missing? Or might might try to use the wrong partition. But then you can use the replace command on the right new partition. RAIDz1 is supposed to handle a single drive failure (but you data is at risk as you lose redundancy).
Don't run both. Run the one that is applicable to your setup. Read the manual about proxmox-boot-tool first to determine if your Proxmox uses it. I'm assuming your run PVE 9.x but you might be on a much older version.
Or you can just do nothing and leave it as it is fine this way. Since you do not boot from those drives (in your non-standard setup that you chose). Don't rely on me for any guarantees as I'm just a stranger on the internet that might not have your best interest at heart. If you want professional support your can buy a Proxmox support subscription or get a Proxmox partner to help you.
Maybe create a test server and experiment/learn about all this first? Or create a VM that looks like your production server and practice this first?
