In a word, yes. Some relatively rare phones such as Pinephone and Librem have actual power switches, and maybe some others actually go off. The vast majority of consumer phones appear off but are still calling home to the mother ship. Many diagnostic test have been done and published to prove this. If you really need it, I could probably go find them for you.
Thanks. I'm guessing this is when happened when hardware vendors stopped making phones with removable batteries then? I would be really interested in any links you might have yes. I did a cursory search but came up with little more than a stackexchange question.
Both Ithings and Google devices have a find my phone feature that works even when the phone is off. That is something you can test yourself if you have one. Obviously for this to work, the phone is sending its location even when it is supposedly off. It seems that the company in this reporting is not getting data from Goopple yet, but those who are really concerned about not being followed are careful with this and use different operating systems. https://www.xda-developers.com/iphone-findable-turned-off/
