I suspect that there may be some miscommunication due to using different versions of the PHB. Also, I'm open to being corrected if wrong. So, I pulled out my old 5e PHB to compare it to the new 2024 version.
"Help" as a specifically named action is described as a combat action in 5e2014. That can be found in Chapter 9, page 192 of the 2014 PHB.
However, you can still help another character outside of combat. In the 2014 PHB, this is described as "Working Together" on page 175 of the 2014 PHB.
The 2014 PHB says that a character can only provide help if the task is one that they could attempt alone. As you can attempt (roll a perception check) to see something alone, that would seem to imply that you could work together.
That being said, the example given of picking a lock is an example in which both characters require proficiency in lockpicking. That might imply that something extra is needed for perception. I don't believe that to be the case for perception though because D&D characters are not typically required to specify that they are proficient in using their own eyes.
Though, in the case of darkness, having Darkvision is kinda proficiency in being able to see when others could not. So, I may be inclined to rule that the assisting character must have some extra-sensory way of aiding the character doing the perception.
The entry later says that working together is only possible if multiple characters working together would be productive. I believe that two people specifically observing the same area for the same things would be productive, but I acknowledge that others do not agree with that.
On page 178, the description of how Perception works along with the Finding A Hidden Object sidebar appears to lend credence to the idea that a character could specify to the DM how/where they are looking in situations where the specifics of how you are attempting to perceive something matters. My view is that specificity would matter for working together with someone.
I could buy that the Group Checks entry might apply to navigating a dungeon using Darkvision.
In the 2024 version of the PHB, "Help" is not defined as a combat action. It is defined as an action that can be taken in the game. Later, the rules glossary explains what that does both for attacks (combat) and for ability checks (not specifically combat). "Help" is listed on page 15; the rules glossary is at the back on the book.
Further, the 2024 PHB specifies that using a skill is an Ability Check that gets to add proficiency bonus (assuming proficiency in the skill). It also specifically states that an Ability check can still be attempted even if a character does not have proficiency. I'm paraphrasing a little, but this can be found on page 13 of the 2024 PHB.
Page 19 of the 2024 PHB mentions how light and visibility impact perception. In dim light, you get Disadvantage.
2024 doesn't contain the same restrictions found in 2014 language (that may or may not have applied).
Darkvision, Dim Light, and Lightly Obscured are all defined in the 2024 Rules Glossary as giving Disadvantage.
Help is defined as giving Advantage.
In 2024 PHB, Advantage and Disadvantage cancel out, the same way they did in 2014.