EAP-SIM/AKA authentication using eSIM

That is indeed a very good question...However, I don't think you can instruct iOS to do anything related to EAP-SIM unless you are a wireless carrier, in which case Apple will tell you exactly what to do. Otherwise, you can specify actions for EAP-TLS/TTL/PEAP, but not EAP-SIM. https://developer.apple.com/documentation/networkextension/nehotspoteapsettings/eaptypeIf I had to guess, I would say that it will very likely use either SIM or eSIM which is assigned to a "Primary Line" in settings and which currently has an active data connection. It is very unlikely to search through possibly multiple eSIM profiles to check if one would authenticate.

Thanks for your opinion. I think I agree with you on what it may do.

Just one point, You can setup EAP-SIM via a mobileconfig, but there is no published content within that configuration to specify the SIM or the carrier PLMN.

If it is a HS2.0 network then the PLMN will be in the ANQP so it should know what to do, but if it is not HS2.0 then I suspect that in this case you are right, it would just try to authenticate with the default data SIM. However that can result in the radius server dealing with an incorrect authentication from a SIM which is not its own (and I wonder if it would do it and fail 3 times over!).

You are probably also right that if you are a carrier and doing this, all of this can probably be specified. At least I hope it can for the sake of the AAA.