I know [similar](https://apple.stackexchange.com/questions/374788/unmounted-volume-asks-for-password-at-login) [questions](https://apple.stackexchange.com/questions/301023/how-to-prevent-an-encrypted-apfs-volume-from-automatically-mounting) [have](https://apple.stackexchange.com/questions/39344/is-it-possible-to-disable-auto-mount-of-external-devices
) [been](https://apple.stackexchange.com/questions/367942/how-to-auto-mount-a-secondary-encrypted-hdd-on-boot
) [asked](https://apple.stackexchange.com/questions/310574/how-to-prevent-auto-mounting-of-a-volume-in-macos-high-sierra
) [before](https://apple.stackexchange.com/questions/361523/how-to-prevent-auto-mounting-of-encrypted-apfs-volumes-by-diskarbitrationd
) but I just can't believe this can't be solved, so I am going to ask again with specific details.

I have two partitions that are bootable on the internal drive of my Mac running macOS Catalina 10.15.7. Both are encrypted APFS volumes.

Whenever I log in to one of them, I am getting a promt, asking me for the password of the other. I do not want to **store the password in the keychain** to work around the prompt (for security reasons), in fact I do not want the other volume to be automatically mounted at all.
All I want is to be able to **choose the boot volume on startup** (via the [Opt] key).

---

I tried 

1. adding this line to my `/etc/fstab` using `vifs`:

```
UUID=<UUID of the volume> none apfs rw,noauto
```
but this does not prevent the prompt from appearing.

2. changing the volume role via 
```
diskutil ap changeVolumeRole <diskId> D
```
but this returns the error: `Error setting APFS Volume role: Unable to set the APFS Volume Role (-69599)`

---

Is there seriously no way of preventing disks from being automounted? 
Can the Finder be at leat taught to not ask for the password?