The more I think about it, the more the Invisible condition doesn't work for me. I think it's badly named, sure, but I think the entire point of the condition has too many areas where it falls apart.
One of the things that sort of annoys me about "Invisible" is that it's an all or nothing affair. Either you're hidden from all enemies, or from none of them. For simplicity's sake, that's fine. But imagine if the party has (say) Gollum following them and they're hiding from some orcs. They don't know that Gollum is there, but every hide attempt against the orcs fails because Gollum is an enemy that can see the party.
Apart from simplicity, the mechanical benefit to being "invisible" is that you get advantage on your initiative. I'm not so sure this is worth the weirdness it creates.
I was talking to Teos "Alphastream" Abadia about the passive Perception thing earlier, and his interpretation of the changes to the passive Perception rules (and their removal from the Hide action) was that monsters don't get to use passive Perception to detect you. That isn't my interpretation, but I'm still rather confused about how they interact.
In 2014, it was very clear. Passive Perception was baked into the Hiding rules. In 2024, it very much feels they're walking back from that. Which is where I get confused with the Dragon with the passive Perception of 25.
If passive Perception still works as it did in 2014, then you'd make your DC of 15, you'd say "Hooray, I'm Invisible!" and then the DM would say "The Dragon now detects you, you lose the Invisible condition".
If passive Perception doesn't work at all, then you'd make your DC of 15, you'd say "Hooray, I'm invisible!" and the Dragon would have to take the Search action (often one of its Legendary actions) to find you.
But there's also an in-between state where passive Perception works, but only when you do something after you're hidden. And I have no idea what the timing on doing that is. (Do monsters get passive Perception checks for free on their turns?)
This is one of the reasons I really wished the DMG spent time talking about hiding and stealth in D&D and how to rule various situations and make fun gameplay from them.
Cheers!