The #tfc:bypasses_damage_resistance damage type tag does not work, all damage types are still reduced by TFC's resistance system.
I first encountered this issue whilst trying to add new damage types to the tag.

A great example of this bug is the fact that magic damage, included in the #minecraft:bypasses_armor tag used in the TFC tag still gets reduced by TFC armor.

https://cdn.discordapp.com/attachments/859316125958930462/1399906379828826226/Minecraft__Forge_1.20.1_-_Singleplayer_2025-07-29_21-07-11.mp4?ex=688ab3e9&is=68896269&hm=71e01b23fa5c16fe4c547c306b71f4ed7147785409e252be309cb2563e996d9f&