Things I would add to the rules to clarify what I believe is either the intent, or the expectation of how things work:
1) Add an "Unseeable" clause to Invisible:
Unseeable: If you gain the Invisible condition via a magic action, or via a feature which grants "magical" invisibility, you cannot be seen with normal vision.
This would be similar to breaking Invisible into Invisible/Hidden, and giving Invisible the Unseeable trait + Hidden condition. I just think the trait in the condition is better streamlined than multiple conditions. It also avoids having to include the verbiage in every single location where magical invisibility is granted.
2) Better define "enemy", and when a creature qualifies as an enemy. This can get complicated, though, so at best it would be something in the DMG, and not in the PHB. This may also help define "find".
2a) When elaborating on "find", note that a creature can only find you on its turn. This gives the implicit result that you only have to end your turn behind cover to help prevent you from being found.
3) Have additional actions that can grant the Invisibility condition. The "make a sound louder than a whisper" only really works as an end condition when you're trying to be quiet and not seen, where being noticed at all is a failure state. (Also, someone has to be close enough to hear for it to matter.) While conceptually the rules support a much broader scope, the specifics don't always match the expected narrative.
So, for example:
Disguise: Make a Dexterity or Charisma (Disguise Kit) check, and if you beat a DC of 15 you have the Invisible condition. (A suitable, already-prepared disguise may substitute for the Disguise Kit.) The condition ends if an enemy finds you, you make an attack roll, or if someone sees you act in a way inconsistent with the creature or person you are attempting to impersonate.
- Example: Luke and Han in stormtrooper outfits.
Blend In: You blend in with a crowd. Make a Charisma (Stealth) check, and if you beat a DC of 15 you have the Invisible condition. The condition ends if an enemy finds you, you make an attack roll, you behave in a way that causes the crowd to reject you, or you leave the crowd you blended in with.
- Example: Imhotep! Imhotep!