I have two MacOS installs as part of a dual-boot configuration on my MBP. Both happen to be Mojave 10.14. They are installed on two encrypted APFS volumes in the same APFS container.
I want to be able to set the next boot volume without supplying a decrypt password or holding down the option key during reboot. Related, I want the current 'other volume' to be the default volume. The current default is the second MacOS install that I performed.
The troubles I see:
1) Under System Preferences -> Startup Disk is that the decryption password is needed: "It must be unlocked to determine if it is a valid startup disk." - this can't technically be true. When I hold down the Option key during boot the decryption passwords aren't known at that time yet two volume options are presented.
2) The examples of command-line bless command are based on a volume mounted under /Volumes which of course means the decryption password is made available.