Many MVNOs had eSim capability for awhile, depending on the carrier.All MNVOs I've checked in the U.S., including the one I use at the moment, all have had eSim support for a while. What you might be confusing eSim support with is the eSIM Quick Transfer. My transfer was instead done in the MNVO's own app and took less than a minute to generate a new eSim, invalidate the old Sim, and add the new eSim to my phone.
Edit:
For anyone who is curious:
Carriers with eSim Support in U.S., as listed by Apple:
- Appalachian Wireless
- AT&T
- Boost Mobile
- Carolina West Wireless
- Cellcom
- Chat Mobility
- Consumer Cellular
- Copper Valley Telecom
- Credo Mobile
- Cricket
- C Spire
- FirstNet
- GCI
- H2O Wireless
- Metro by T-Mobile
- Mint Mobile
- Nemont
- Nex-Tech Wireless
- NorthwestCell
- Optimum Mobile
- Pioneer Wireless
- PTCI
- PureTalk
- Red Pocket
- Republic
- Spectrum Mobile
- Straight Talk
- Strata
- Thumb Cellular
- T-Mobile USA
- Tracfone
- Truphone
- Ubigi
- Union Wireless
- United Wireless
- US Cellular
- Verizon Wireless
- Visible
- West Central Wireless
- Xfinity Mobile
Xfinity Mobile had it last year with the iPhone 13 models but their current website states that it's available 'now' for the iPhone 14 models.
Some time ago, brought in the 13 Pro to a local Xfinity store. The store manager himself said they were seeing issues with eSim and the iPhones. Those problems went away when they used the physical sim cards.
Lots of people on various online boards are reporting issues with using the eSim in their iPhones. Apparently, even though MVNOs have the capability for eSim, they are going through growing pains with a massive rollout of eSim on their systems which can't handle it properly.
Apple has forced the American cellular companies to rely on eSims more, starting with the iPhone 14 so it'll take some time, to say the least, for those American companies to get their infrastructure fixed to handle eSim capability. That is also a warning to international companies that Apple is planning on moving to eSim for future iPhone models so those international telecom companies better get their infrastructure ready, most likely by next year with the next iPhone model.
Apple could've made it less of a mess by literally advertising the fact of their eSim adoption policy but didn't due to its strict privacy policy on their products. That's a major failing on Apple's part as it continues to force consumers and companies to what Apple thinks should be done.