That sounds like a hardware limitation more than anything.
According to one of OP’s follow-up comments, he says that it works if he puts a random SIM in without service on it, so it’s not a limitation on his phone, at any rate.
EDIT: Actually…hmm. Now that I think about it…was I using Bluetooth tethering on my phone at the time rather than a WiFi hotspot? I was just remembering being startled that the phone would link the laptop to a WiFi network, and I’d used multiple approaches (WiFi, Bluetooth, USB) to link the phone at the time.
According to one of OP’s follow-up comments, he says that it works if he puts a random SIM in without service on it, so it’s not a limitation on his phone, at any rate.
EDIT: Actually…hmm. Now that I think about it…was I using Bluetooth tethering on my phone at the time rather than a WiFi hotspot? I was just remembering being startled that the phone would link the laptop to a WiFi network, and I’d used multiple approaches (WiFi, Bluetooth, USB) to link the phone at the time.