How does the phone manufacturer have anything to do with it? My only wish is to support multiple eSIMs, as now I only have one physical SIM slot and one eSIM.
A physical SIM in contrast always works. I was already questioning whether I'd ever need to upgrade from the 12 Pro but this type of needless regression makes it an easy decision.
You could still get everything working by manually configuring the phone, and carriers like GiffGaff had support articles explaining how, but it was a total pain in the arse and stuff would occasionally break in subtle ways.
Additionally the eSIM is separate physical chip within the phone attached to baseband radio. Once configured with a profile, the host OS has as much access as it does to a normal SIM, I.e. not much. The entire standard is kinda a hack, which basically boils down to “what if we embedded a normal SIM card chip in the phone, and let the phone flash a new carrier profile every now and then?”. Remember these SIMs are fully fledged computers, like their normal removable counterparts, that can ignore host OS commands, and issue instructions directly to the baseband processor without the host OS knowledge.
Then there’s the dozens of companies in the App Store like https://www.dentwireless.com/ who all provide eSIMs for international travel. I find it hard to believe they all have agreements with Apple, it normally costs far to much to deal with Apple for bottom dollar companies to make any money.
So would take all of those sources with a large pinch of salt. If Apples eSIMs we’re proprietary, I would expect to be easy to find articles discussing the fact, given they’ve been around for a few years now.