The description of Truesight says:
A monster with truesight can, out to a specific range, see in normal
and magical darkness, see invisible creatures and objects,
automatically detect visual illusions and succeed on saving throws
against them, and perceive the original form of a shapechanger or a
creature that is transformed by magic. Furthermore, the monster can
see into the Ethereal Plane within the same range.
The True Seeing spell description says:
This spell gives the willing creature you touch the ability to see
things as they actually are. For the duration, the creature has
truesight, notices secret doors hidden by magic, and can see into the
Ethereal Plane, all out to a range of 120 feet.
The Detect Magic spell description says:
For the duration, you sense the presence of magic within 30 feet of
you. If you sense magic in this way, you can use your action to see a
faint aura around any visible creature or object in the area that
bears magic, and you learn its school of magic, if any.
Though I realize these are different things, I cannot help but notice the common trait of the awareness of magic within, or around objects or creatures. While Truesight and True Seeing seems to unravel the magic and is able to see beyond it, Detect Magic is only able to sense that something is magical until it uses an action. Given that all three have awareness about the magical world, would a creature that has truesight, or one that has True Seeing cast on it, also be able to tell if a weapon or object has a magical property or not?
Best Answer
Truesight does not directly give awareness of magic
It's important to note that while truesight allows a creature to see through any kind of magic that hides the true form of something, it doesn't "highlight" the magic that is doing the hiding. For example, if you find a door that is hidden by magic using truesight, you don't automatically find out that the door was magically hidden, you just notice the door when you otherwise would have failed to see it. Similarly, if you peer into magical darkness and see an object you otherwise couldn't see, you don't automatically know that the object was hidden by magical darkness. In fact, with truesight, you probably couldn't easily tell the difference between magical and mundane darkness.
So, unlike detect magic, truesight does not directly tell an observer what is and is not magic. Instead, it shows things as they really are and reveals any illusions as false, and the observer must make their own inferences about what might be magic based on discrepancies in what they see. In particular, any magic that does not create an illusion or hide or obfuscate the true form of something will appear the same with and without truesight.