A current iMac 24 is surprisingly lightweight compared to what it replaces. My 2011 21.5 is distinctly heavier than the current iMac 24. That said an Apple Studio Display feels heavier than the iMac 24, but maybe not as heavy as my 2011 iMac.The biggest pain I had with my 2012 27" iMac was when I had to take it to the Apple Store for a repair. If I recall it had something to do with the power supply. The screen wise fine. Anyway, the store was in the middle of a mall, and I had to haul that thing from the parking lot and halfway through the mall to get to the store. I then had to replay that scenario in reverse when I had to pick it up after repairs a couple days later. Besides its size, the weight distribution of that machine makes it awkward to carry.
I loved my iMac, but will never buy an AIO ever again. It's just too big and bulky for my taste. Since then, I converted to a Mac Mini, and now a Mac Studio, both attached to a pair of 27" monitors, the same monitors which I will probably continue to use for years to come.
It has been said that one of the concerns over the current iMac is its light weight could make it vulnerable to easily knock over or off a desk. The older iMacs were less prone to that risk because of their weight. Remember the awkward weight of the G3 iMacs and G4 eMacs. At least the G3s had a handle.
The general trend with AIOs, like laptops, is toward being lighter overall.