Prevent encrypted APFS volume on partition to automount / ask for password on login - Catalina
Starting with MacOS BigSur 11.1. the /etc/fstab/ solution works (again):

find the volume label from the volume name:
diskutil list | grep &lt;volume name&gt;
the last entry (e.g. disk2s2) is the volume label.
find out the volume UUID from the volume label
diskutil info &lt;volume label&gt; | grep &quot;Volume UUID&quot;
open /etc/fstab for editing:
sudo vifs
add a line preventing the auto-mount of the volume:
UUID=&lt;volume uuid&gt; none auto noauto

Here's a complete example:
&gt; diskutil list | grep &quot;Macintosh HD2 - Data&quot;
2:                APFS Volume Macintosh HD2 - Data⁩       341.8 GB   disk2s2

&gt; diskutil info disk2s2 | grep &quot;Volume UUID&quot;
Volume UUID:               C58A1BDC-593C-4854-B954-702A73ABD67C

&gt; sudo vifs
# add the following line:
UUID=C58A1BDC-593C-4854-B954-702A73ABD67C none auto noauto

On the next reboot the popup asking for the password will no longer appear.