I think you haven’t told the whole story.
Are you installing a v6 snap because you are trying to have both v6 and v7 on the same machine? Where did you get it? I don’t see any more v6 snaps, maintainers have moved to v7.
Or are you installing a v6 snap because you can’t find normal v6 packages?
Do you really need v6? If migrating from v5 you can go directly to v7 now that the importer bug has been squashed.
A snap is a squashfs image and mounted by the snap subsystem. For example I have the Open Watcom snap on my machine:
/dev/loop1 50M 50M 0 100% /snap/snapd/18596
/dev/loop0 56M 56M 0 100% /snap/core18/2721
/dev/loop2 86M 86M 0 100% /snap/open-watcom/2
and the mountpints are:
/var/lib/snapd/snaps/snapd_18596.snap on /snap/snapd/18596 type squashfs (ro,nodev,relatime,errors=continue,x-gdu.hide)
/var/lib/snapd/snaps/core18_2721.snap on /snap/core18/2721 type squashfs (ro,nodev,relatime,errors=continue,x-gdu.hide)
/var/lib/snapd/snaps/open-watcom_2.snap on /snap/open-watcom/2 type squashfs (ro,nodev,relatime,errors=continue,x-gdu.hide)
If the v6 KiCad snap is less than several hundred MB then it probably does not include the 3D models.
Is the path /usr/share/kicad/symbols
as observed from outside the snap or from within the snap? If outside then you are probably looking at the v7 libraries if you have v7 installed. If inside, then it is mapped to /snap/kicadsomething/current/<some library path>
using bind mount.
So to provide 3D models to the snap you have to install the 3D model library, and then make it accessible to the snap (I never looked into this myself) but here are some ways: How to give snaps access to /somedir - Ask Ubuntu