I used to do this on long flights, but most in flight providers have stopped trying to identify and shape specific protocols and now limit bandwidth purely by client. If you get a few people on all at once it thinks you are streaming video and throttles you.

This is how we get aircraft wifi with Meraki Air Marshall-like DDoS [0] for hotspots. Don't ruin it for us!

[0] https://documentation.meraki.com/MR/Monitoring_and_Reporting.... This basically detects any access points in a wireless network repeating a signal and automatically boots them. only works on 2.4GHz networks if I understand correctly.

... wouldn't that be a type of jamming and therefore illegal ?

Doesn't stop hotel chains from doing it

I believe that you can't both simultaneously provide wifi hotspot and use wifi internet (at least, I couldn't on a phone several years ago last time I tried it). I think you can only do that if the network the phone is using is accessed via the cellular modem.

That used to be the case but it has changed now. Probably depends on the phone broadband chipset used.

These days you can passthru your WiFi or even a wired connection (via USB to a connected PC or a Ethernet-to-USB adapter) via a Hotspot.

You can on Android, and have for some time IIRC. This is how I get free wifi on my computer by passing it through my T-Mobile phone.

I absolutely can, that's how I connect my ps4 to my uni accommodation internet as it's mschapv2 or smth the ps4 can't connect to. I know it's definitely using the wifi and not my mobile data as my data usage for the day is unchanged after I've downloaded a game.

Cheap Chinese android phone from 2020 (or maybe 2021 can't remember).

Correct. My GL-E750 Mudi has a repeater function:

https://docs.gl-inet.com/router/en/3/setup/gl-e750/internet/...

My iPhone does not.

Depends on the phone OS and wifi chipset Some Pixel phones can do it last I checked, which was about a year ago. It's a fragile dependency. For example, a Samsung with the same wifi chip didn't work.