>>...mobile subscription is from the same provider as my broadband internet connection...I’d rather not rely on the mobile hotspot

For the mobile connection, it's a matter of what backhaul connects to the tower you're using. Simple enough to use traceroute to see what commonality might be there. A matched pair of IPs probably indicates a shared trunk. One or both of those might be in a geolocation database, so you'd have a hint as to how far away the commonality might be.

You might also assess the probability of Starlink's long term survival. They need a lot more sats and subscribers, and it's not clear to me they'll get permitting. If you're OK with the latency of geosynch, Hughes looks healthy as it is (you're stationary, so a one-time installation of a parabolic antenna and you're done)

I do similar. I have two ISPs. One is to a campus-wide net in my community that is on FIOS and Comcast. The other is a direct FIOS connection (community and personal FIOS both land in the same central office, but residential Comcast has variable congestion issues - community can afford connection w some guaranteed nines - long story)

As a side note, your mobile provider might sell plans to stationary locations. Verizon does that here. It's cheaper as it's more predictable for them. I've been considering it as a tertiary. pfSense lets me fail-over between as many ISPs as I want, giving each a priority. Ditto on routing. I haven't bothered as it seems unnecessary - but I have set up some clients with 3 ISPs (loss of VOIP would be costly for them).