I would guess that the objects that you downloaded have a super high polygon count. My biggest complaint about Google Warehouse, and most 3DS/etc 3D object sites, is that the total size and polygon count of the objects is not given - you don't know whether they are good (and lightweight) or terrible until you try using them.
Do things perform normally if you delete the balcony objects?
Go to Help > Downloads to download the Polycount add-on, if you do not already have it installed. Relaunch Archicad and check the polycount for those balconies. (The Polycount add-on will list the counts for every object, as well as totals.)
Cheers,
Karl
AC 28 USA and earlier • macOS Sequoia 15.3, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
One of the forum moderators