Summary:
As of version 1.20.40.20, foxes cannot pick up non-stackable items (like swords, armor and totems).
This happened after fixing MCPE-173898 - an issue where foxes could not pick up equippable items. - (before this issue MCPE-173898 (version 1.20.30.20) foxes picked up items correctly except for MCPE-153135 when foxes automatically places items in armor slots).

Steps to reproduce:

1. Summon the fox.
2. Throw the fox a non-stackable item (like swords, armor and totems).

Observed results:
Foxes ignore the item.

Expected results:
Foxes will pick up the item.

Original description:

When I went to get my tamed fox a totem of undying, they didn’t pick it up, but when I went to give them a steak they took it and it doesn’t work for swords either. I hope this is helpful.