Every day I am increasingly glad I switched to GrapheneOS

No OS protects you from this. If you are carrying a device that communicates with cell towers, your location is being triangulated and logged. I’m not sure about the daily location signals they’re referring to, but cell tower triangulation has been a thing for a long while.

Only way to avoid it would be to only carry devices that cannot transmit data. Internetingly enough, pagers fit the bill as receive-only devices. Messages are broadcast on the entire network instead of routed to a single device.

I'm well aware of this, the reason I bring up GOS is because it fully disables your phone's radios when you turn them off, meaning cell tower triangulation and GPS do not work at all unless explicitly enabled.

This as opposed to a typical phone, which leaves GPS on even when location is off and pings towers periodically even when service is inactive.

I personally leave my phone in airplane mode with location/camera/microphone disabled at all times unless I explicitly need them. I use wifi calling so I can still use it as a typical phone and per-connection MAC address randomization (+ a VPN on public wifi) so my device isn't easy to track via IP.

GOS is great for this because I can be reasonably assured that apps are not bypassing my permission settings without my knowledge and consent. (That and I can de-google which in and of itself goes a long way in decreasing trackability)

Isn’t GPS only one way? Is the phone then sending the data to the carrier?

I'm a bit confused by your question...GPS definitely requires communication between your phone and a satellite (i.e. can't track you if your GPS unit is off - maybe you're thinking of satellite imaging?). With wifi calling, yes, data is being sent to the carrier, but not via a signal that can be triangulated, so the most accurate location data they can gather is your IP address, which a VPN can easily hide.

Or do you mean in terms of generalized location tracking? In which case yes, highly accurate location data is shared by your phone with your carrier by default, just by way of how cellular networks function; no GPS required.

My understanding of GPS is your phone uses satellite positions to figure out it’s location. The satellites are not receiving info from your phone/Garmin.