75 GB is missing under 'Other volumes' category
First, nothing is really missing. An APFS container composed in this manner looks like this in Terminal and Disk Utility.

A standard boot volume APFS container in Catalina accommodates five volumes:


a preboot volume (your disk1s2)
a recovery volume (your disk1s3)
a VM volume (your disk1s4)
a read-only mounted system volume (your disk1s7)
a read-write mounted data volume (probably your disk1s1)


The last two are combined in one APFS volume group.



Your container disk0s2 houses two additional data volumes  (disk1s5 and disk1s6) though. Both adhere to the standard naming scheme of the default read-write mounted data volume of an APFS boot container: [name_of_main_volume] &amp; [ - Data]. The larger of the two additional data volumes (disk1s6) is not mounted and therefore "missing".

Considering the size of the various data volumes disk1s6 is probably your former data volume. I assume that it was replaced by the very small disk1s1 data volume in the APFS volume group accidentally.



To solve your problem additional info (as stated in my comments) is required.