From what I can read here
about the connected vehicle/services stuff:
"App Access" plan includes the stuff on
the infotainment system (Google Maps, Google Assistant, Access to Google Play store, etc) and maybe the WiFi hotspot
but the website is a bit unclear on this.
"Remote Access" plan includes the stuff on the My<Brand> App on your smartphone (door lock/unlock, flash lights, locate vehicle, vehicle status, etc)
"App Access" appears to cost $11.99/month
"Remote Access" appears to cost $11.99/month
You can bundle these two into "Connected Vehicle" for $22.99/month. This appears to include the WiFi hotspot as well.
There appear to be discounts for a paying a year in advance (Seems to be about 12 months for the price of 10 or 11).
Then, if you also want to keep the OnStar suite of Safety and Security services (the stuff you get when you push the blue OnStar Button), from what I gather here
about those services:
You also need to add in the appropriate
Connected Vehicle, Safety and Security, Essentials, or Premium
Note, this overlaps w/ the info about about App Access + Remote Access, which implies there is a discount for connected vehicle...
Now, as for what you could do if you let it all go and connected to your phone's hotspot...that one is a bit more unclear...someone said it does work to support the infotainment unit's data needs. But...if you are going to let it all go, I would think at that point, just go with using CarPlay or Android Auto and yoru infotainment system becomes an integrated display, and not much more.
I also am a bit curious how well the SiriusXM experience is if you don't have a data connection...as I think some of that function is pushed to the cellular connection, based on what I can see; because there are channels/channel numbers not available in my wife's Honda Sirius XM tuner that is a vehicle that is not a "connected vehicle".
Perhaps someone w/ an expired trial can comment...my trial was for 3 years on the Connected Vehicle and Data. 3 Months on the OnStar, which I have renewed to Safety and Security.
Here is a screen snap of what my GMC account looks like for my vehicle (with appropriate redactions):