I think the my.smartthings.com is the only way to get more than 20 rooms. Both Android and iOS won’t let me add anymore…I have had to go into the web page to do it.
I don’t think I got to 20 rooms…certain not more, since I’ve only created rooms using iOS. But, I have hit the magic number (>15). Where new devices now show up under “Living Room” rather than the “No room assigned room”… I think I peaked at 17 or 18, but have trimmed to 13 rooms now (yet location is a 300 square foot studio apartment…)
“Living Room” is the the most crowded room, and new things are inserted randomly into rooms (both when created/discovered or moved.) So sometimes, even when I know its going to be in “Living Room”, its a challenge finding it (after seeings it not at the nd of the room list…especially when its supposed to be sorted alphabetically.