Now, suppose they roll a total of 25. Inside the room, you have a secret door with DC 20. Can't the roll justify that whatever the character was actually doing while "perceiving" resulted in them finding the secret door???
this is the part that drives me nuts
a DM made a room with a secret a PC may or may not find.
the DM has a set DC of XX (we are calling it 20, that's high in one of my games but not unheard of)
the player has a relativity low passive perception of 13 so they open the door and the DM describes the room with out saying anything about the secret.
the player already used player skill in some way by saying they wanted to actively look. (BTW one of those ways that player skill is mitigated and minimized is the passive score, if they had a wis 20 and +3 prof and the alert feat that would be a passive of 23 and the player would not have to actively look just walk in ot the room... maybe it is observant not alert that gives the +5 i have to check now)
the player relayed they want to make a perception check and that they want to look carefully... I see 0 reason not to roll (a hard check at that) to see if they notice it...
(((BTW I once played in a game as a druid with a godyl 23 wis and trained in perception so my passive was 19 then up to 21 at one point... but we had another PC that had the slightly less godly 21 wis, and was a rouge (i think it is called inquisitor or investigator or something) based on sherlock homes and he had expertise and the +5 feat... so his passive was 23-30 at those same levels. every room we walked into the DM would have fun describe 3 time once for 4 pcs, then he would say I got all that PLUS and always had at least 1 thing sometimes 2 or 3, then he would tell the rogue player he saw all that plus 2 or 3 more things... and like I mean just open door everyone gets room description, I get a secret door and a trap, the rogue got all that plus a hidden mimic and a small bit of blood... it was hecka fun, and I promise you he (the rogue) multi times just called investigation, insight, and perception skills with no fluff just 'my character sees things i don't even know to ask for'))))