My Neotech 4" strap does NOT stretch now (though they say it does, and maybe it did when new -- I think it's the memory foam in it that gives that impression) https://www.neotechstraps.com/mega-strap.html , but the one my brother suggested I get DOES stretch a little. It's called a Comfort Strapp. Comfort Strapp™ – Comfort Strapp™ Guitar Straps It is indeed comfy. It's on the Squier VM Jaguar SS that I don't play (mostly because the Jazz-size neck makes my hand crampy after a while), but the strap is fine. I do prefer the Neotech, though.
I think that the width to distribute the weight is most important, I don’t notice any stretching other to conform to the anatomy that it sits on. No yo-yo’ing. But neoprene is a rubber and with age can change and even break down.

