The boots "The speedy Lightfeet" are considered as medium armor and warns for non-proficiency when equipped but have no in game effect.
![[Linked Image from i.imgur.com]](https://i.imgur.com/eGSbap6.png)
you can still cast the spells and sneak attack while wearing them if not proficient.
![[Linked Image from i.imgur.com]](https://i.imgur.com/pxjlN3r.png)
![[Linked Image from i.imgur.com]](https://i.imgur.com/2j9nG73.png)
while wearing actual medium chest piece armor spells are not able to be cast but sneak attack i still possible even if it gives you disadvantage on the attack.
![[Linked Image from i.imgur.com]](https://i.imgur.com/I168jyp.png)
![[Linked Image from i.imgur.com]](https://i.imgur.com/g3RqQCu.png)
![[Linked Image from i.imgur.com]](https://i.imgur.com/pUC7hK8.png)
the same logic applies to helmets, gauntlets and boots that are tagged as light/medium/heavy armor but does not impede the unarmored perk for the barbarian.