The fact that newer phones (Pixel at least) can use WiFi (client mode) as the WAN/uplink side of its hotspot stack (NAT, AP, etc.) is pretty neat. Not long ago, only the cell modem could serve in that capacity, as far as I'm aware. Frankly I'm surprised a single WLAN radio can pull that off. I pay the $8 on my phone and share it to my laptop and whatever devices my travel companion(s) might have.
Windows has been able to do exactly this since Windows 7! It's called Wireless Hosted Network[0], and if you've ever seen the "Microsoft Virtual WiFi Miniport Adapter" (Windows 7) or "Microsoft Wi-Fi Direct Virtual Adapter" (Windows 10/11) in your list of network adapters (it may be hidden), it's there specifically to enable making a hotspot while being connected to a wireless network.
> Maybe at the cost of latency because it has to switch channels back and forth?
Not necessarily. It can be a client on 2.4Ghz and an access point on 5Ghz. Even without that, if it has MIMO, then one of the antennas can be receiving 2.4Ghz while the other is sending (at least in theory, if the crosstalk between the antennas is low and the selectivity of the receiver is sufficient).
Most laptops can't do this, right?