I have one installation of Open Indiana on the disk sdb and i tried to mount it with the command suggested by you and it didn't work.
root@Z390-AORUS-PRO:/home/ziomario# fdisk /dev/sdb -l
Disk /dev/sdb: 465.76 GiB, 500107862016 bytes, 976773168 sectors
Disk model: Samsung SSD 860
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x0544649f
Dispositivo Avvio Start Fine Settori Size Id Tipo
/dev/sdb1 * 25088 976751103 976726016 465.7G bf Solaris
root@Z390-AORUS-PRO:/home/ziomario# sudo mount -t ufs -o ufstype=sun /dev/sdb1 /mnt/sdb1
mount: /mnt/sdb1: wrong fs type, bad option, bad superblock on /dev/sdb1, missing codepage or helper program, or other error.
root@Z390-AORUS-PRO:/home/ziomario# mount -t ufs -o ufstype=sun /dev/sdb1 /mnt/sdb
mount: /mnt/sdb: wrong fs type, bad option, bad superblock on /dev/sdb1, missing codepage or helper program, or other error.