What's happening
ADHD and tidying a room can turn into a tour of the whole house. You pick up a mug in the bedroom, take it to the kitchen, spot the washing-up and start on that. While you're there, you notice the bin's full. An hour later, the kitchen's half done, the bin's still full and the bedroom looks exactly the same. Every item that belongs somewhere else is a ticket out of the room.
How to get moving
Before you start, put a laundry basket or a big bag in the doorway. Anything that belongs in another room goes in the basket, not back to where it lives. Put a bin bag next to it for rubbish. Now there's no reason to leave the room until the room's finished, and nothing to lead you off into the kitchen.
Start at the door and work round clockwise, one surface at a time, so you're not darting about after whatever catches your eye. If you remember another job, like booking the boiler service, say it into a note on your phone and carry on. If the room feels big, set a 20-minute timer and let yourself stop when it goes.
Important tip
Only empty the basket once the room is done, and treat it as a separate job. Walk it round the house and drop each thing in the right room without stopping to tidy anywhere else. If the basket doesn't get emptied today, that's fine. One clear room and one full basket beats five half-tidied rooms, and you'll know exactly where to look for anything you've moved.
This is lived-experience content. It is not a promise that a particular idea will work for everybody.