Fixed in Oracle Solaris SRU 11 (Hardware Management Pack for Oracle Solaris version 18.104.22.168).
On systems with Oracle ILOM version 3.2.6, attempting to run the ubiosconfig command to change system UEFI BIOS settings will fail with an error message about being unable to connect to the BMC. This issue has not been seen in other versions of Oracle ILOM.
To make changes to UEFI BIOS settings for these systems, you must run the system's BIOS Setup Utility either at the local server console or from a remote console. Refer to your platform documentation for additional information on accessing the BIOS Setup Utility.