Proxmox’s “ZFS over iSCSI” plugin doesn’t support the iSCSI targets used in TrueNAS (scst in SCALE, ctl in CORE) - and to muddy the waters, by enabling the SSH access directly from Proxmox it might have accidentally made some unwanted changes on your TrueNAS machine as @awalkerix alludes to. Might be worth looking at the output of zfs history from a shell on your TrueNAS machine and see if it’s been creating new zvols or datasets.
For sharing to Proxmox, you can either configure LVM on a shared iSCSI extent, manually provision the LUNs yourself, or use a community-created Proxmox plugin: