wrote:

I suppose that being Hyperglide chains, Shimano only intends for them to be
used with 6/7/8 speed Hyperglide sprockets. I guess Hyperglide's ramps
take over the role of protruding pins snagging adjacent sprockets when
shifting.

In practice, I find that 8-speed compatible modern chains usually shift better on ancient freewheels than old style chains did. Whether that's due to increased lateral flexibility or beveled sideplates or both, I don't know.

My daily rider these days uses a Z72 8 speed chain, a Suntour 14-38 5 speed freewheel, a Microshift 9 speed rear derailleur, and Shimano 6 speed index thumbshifter. It all works fine together, which is more than you can say for a lot of newly produced stuff.