As an ex-player of D&D 3.5, I'm a little bit confused about Adamantine armors and Mithral armors. In 3.5e, they are not inherently magical; it is just classic armor with a different material, so they can have magical properties.
However, in 5e, it seems they are considered magic items in some ways, but not in others; see the accepted answer to "Are weapons and armor made of Mithral or Adamantine considered magical?" for an example.
Can adamantine or mithral armors have magical properties (+1, for example)?