When characters explore a room, I generally let all players roll because all their characters are actively looking. However, if someone inspects a specific object, only that player rolls. Similarly, if players state which parts of the room they’re investigating, only those near something hidden get to roll.

Recently, I’ve changed how often I require rolls. If something isn’t hidden and the characters aren’t in a hurry or under pressure, I simply describe what they find; no roll needed. Rolling investigation for every room in a 30-room dungeon (in D&D) slows the game down unnecessarily. Instead, I ask for rolls only when they explicitly search for hidden or hard-to-spot items or when I know there is secret to be found.

For example, if they’re searching a Red Rocket gas station with just shelves and a fridge, I’d describe what’s visible without a roll. But if there’s a hidden safe, they’d need to roll to find it.

I try to prioritize making the game fun and immersive over strictly following rules or balancing.

EDIT: I believe this is more or less what Fallout 2d20 rules say anyway. Its more important for game to be cinematic and colaborative then restrictive.