There is no legal requirement for that functionality, so maybe some do and some don’t.

However, legal requirements on injury criteria during crash (and specifically head impact to FMVSS208) will have absolute priority and may well conflict with this kind of (ab)use.

Why do you ask? Methinks it’s a leading question!

Most manufacturers will do some form of 'unintended use' load calculation and test for this type.of thing as it's not in their interest to get claims for this kind of breakage under warranty. They could do with employing my brother in law for load testing door and glovebox handles though.....

However, I doubt anyone would be able to put a 100kg downward force on a steering wheel. There aren't many people who weigh 100kg, and of those only very few (strongman contestants) would be capable of lifting their own weight with their arms. Even then, I'd doubt a strongman contestant could lift their bodyweight with their arms out in front of them.

Even if people do hoist themselves in and out of the seat using the steering wheel, I'd doubt whether they put a downwards load on it much more than the equivalent of 25kg hanging off it. If you think how flimsy those grab handles above the door which are designed for that purpose are, I'm pretty sure a steering wheel would cope.