Does the Observant feat allow you to auto-succeed against illusions?

The Observant feat states:

You have a +5 bonus to your passive Wisdom (Perception) and passive Intelligence (Investigation) scores.

To my knowledge, nowhere else in the rules is there discussion regarding a passive Intelligence (Investigation) score.

Furthermore, when added to a character in D&D Beyond, the Passive Intelligence (Investigation) is added under the character’s Senses akin to Darkvision or Blind Sight.

Several illusion spells include language along the lines of:

Can use its action to (do something to see through the illusion) and must succeed on an Intelligence (Investigation) check against your spell save DC.

Does the creation of a Passive Intelligence (Investigation) by the feat constitute a scenario of specific beats general rule whereby any illusion that can be defeated by an investigation check automatically fails if the save DC is lower than the passive score created by the feat?

How to make the Observant feat worthwhile, but not boring, in a 1:1 adventure?

I’ve started DMing a one-on-one D&D 5e adventure. The PC took the Observant feat and as a result, has really high Passive Perception and Investigation (20 and 18 at level 1!). If I use the rules from this question (“if passive perception is higher than the DC, the PC doesn’t have to make a roll to succeed”), then essentially every single perception and investigation check in the scenario I’m running is an automatic success.

In a group setting, that’d be OK:┬áthis makes the PC better at scouting, which is rewarding and fun, and it’s generally nice to be the only/first one in the group noticing things. In a solo adventure, however, I’m afraid that it’s going to be somewhat boring. There’s less of a “wow” effect to noticing small, hidden details when there aren’t people around to be impressed by it.

Should I just stop worrying about it, and simply be OK with my player basically automatically succeeding in every perception/investigation check without thinking twice about it? Or is there a way to tweak the mechanics somehow to make it cooler or more interesting?

Feat Observant: What would balance swapping passive perception bonus for active perception

My DM doesn’t tend to use passive perception of the players, he’ll just get us to roll active perception in most cases. We tend to use perception far more than any other skill in the game.

When a new player joined playing a monk, they wanted to take the ‘Observant’ feat, but didn’t like that the +5 to passive perception would probably not be used. The DM said fine, we’ll just make that +5 to your perception skill, which pushes him to +9 perception at level 2. I’m concerned this overpowers the feat, as he’s already getting an ability point boost from it as well.

How might we change the ‘Observant’ feat so that it’s not useless, but also not inbalanced?

How can Investigation be used passively? (as with the Observant feat)

I understand how Insight and Perception can be used passively: for the DM to determine if an enemy Deception or Stealth attempt is successful without alerting the players that someone is deceiving or sneaking.

But the Observant feat in the Player’s Handbook states:

[…] You have a +5 bonus to your passive Wisdom (Perception) and passive Intelligence (Investigation) scores.

So in what situation would a DM be rolling something against the player’s Investigation without letting them know?

Can you read the lips of a creature a mile away if you have the Observant feat and the level 6 Totem Warrior – Eagle class feature?

A level 6 Totem Warrior Barbarian can choose the Eagle totem, which states:

You gain the eyesight of an eagle. You can see up to 1 mile away with no difficulty, able to discern even fine details as though looking at something no more than 100 feet away from you. Additionally, dim light doesn’t impose disadvantage on your Wisdom (Perception) checks.

Combine this with the Observant feat:

If you can see a creature’s mouth while it is speaking a language you understand, you can interpret what it’s saying by reading its lips.

Using this combination, can I read a creature’s lips, speaking a language I understand, from a mile away?

Is this alternate version of the “Observant” Feat balanced?

I’m a DM and have a player who likes the Observant feat:

  • Increase your Intelligence or Wisdom score by 1, to a maximum of 20.
  • If you can see a creature’s mouth while it is speaking a language you understand, you can interpret what it’s saying by reading its lips.
  • You have a +5 bonus to your passive Wisdom (Perception) and passive Intelligence (Investigation) scores.

However, the player is concerned that it might be hard to remember when to apply the bonus and that the bonuses may be too situational (Only affects passives, references “passive Investigation” which I’ve never seen used).

To try to simplify things, I wrote a homebrew version of the Observant feat using UA’s Perceptive as a guideline:

  • Increase your Intelligence or Wisdom score by 1, to a maximum of 20.
  • You gain proficiency in the Perception skill. If you are already proficient in the skill, you add double your proficiency bonus to checks you make with it.
  • You gain proficiency in the Investigation skill. If you are already proficient in the skill, you add double your proficiency bonus to checks you make with it.

(Basically, it just grants proficiency/expertise for all Perception and Investigation checks rather than a single bonus for passive scores).

Is this feat effectively balanced with the original?