The Invisible condition expressly states that it causes Disadvantage on Attackers trying to attack them, but in doing so, doesn't adjacently make reference to whether the creature in question can see them:
An invisible creature is impossible to see without the aid of magic or a special sense. For the purpose of hiding, the creature is heavily obscured. The creature's location can be detected by any noise it makes or any tracks it leaves.
Attack rolls against the creature have disadvantage, and the creature's attack rolls have advantage.
Note that this is distinct from the section concerning whether Invisible creatures can be seen.
Meanwhile, Truesight obviously permits the ability to see an invisible creature:
A creature 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 creature can see into the Ethereal Plane.
... But it doesn't actually say anything about negating the Disadvantage/Advantage components of the Invisible condition.
What I am forced to conclude is that, while a creature with Truesight is perfectly capable of seeing a creature that is invisible, they would still suffer disadvantage when attacking them, and their opponent would still have advantage against them.
The converse situation is something like Faerie Fire, which specifically handles Invisible creatures with special language:
Any attack roll against an affected creature or object has advantage if the attacker can see it, and the affected creature or object can't benefit from being invisible.
Just as a reference for explaining why I suspect this doesn't apply to Truesight.
Now, to be clear: I consider this to be an asinine ruling. At any table I would DM, I'd be ruling that Truesight does, in fact, negate the effects of the Invisible condition, since this seems more like an oversight/mistake than an intended reading of the rules. But is there something I'm missing, that causes my RAW reading to be incorrect? And if this is the intended outcome, is there a good reason for me to accept it as-is, and not overrule it for my tables?