Actually, compared to many other forum members, I’m not all that knowledgeable about hearing aids and Bluetooth - and whatever I know, I’ve mostly learned from other forum members! 
Most hearing aids of the Big Five or Big Six, including Starkey, use Bluetooth Low Energy if for nothing else, at least for controlling the HA’s via a smartphone app. When I trialed the Phonak Lumitys, which I really liked, even though phone calls and media sound are streamed via classic Bluetooth, there was a separate right and left BLE pairing and connection for controlling the HA settings via the MyPhonak app.
Here’s a list of MFi-compatible HA’s. List of Made for iPhone hearing devices - Apple Support. The list might not be up-to-date with the latest OEM models. Doesn’t have Starkey Genesis or ReSound Omnia on the list, although it has ReSound One - and I know firsthand that the Omnia connects to my iPhone as a MFi HA! 
From what I’ve learned on the forum, one can regard MFi transmission as essentially Apple’s proprietary BLE-like streaming protocol. So, from the list, there are clearly a lot of hearing aids that can employ MFi. And late-developing ASHA is essentially Google’s BLE-like battery-saving streaming protocol that allows many brands of hearing aids to stream directly from Android phones. So, ~everyone’s using something akin to BLE with smartphones. Except Phonak figured out a proprietary way to make classic BT somewhat more efficient, which gives it the great advantage to connect with almost any classic BT device at the cost of some HA battery runtime.
I found the Apple MFi device link on the following page, which is interesting as it offers some opinions as to what HA brands are “most compatible” with an Apple Watch. Perhaps that means the HA OEMs just designed their app to run on the Apple Watch as well as the iPhone.
An article by @AbramBaileyAuD on the main Hearing Tracker website reviews Apple MFi and Android ASHA compatibility and streaming features of hearing aids in 2023:
As Abram’s article ends up discussing, BT LE Audio, whenever it finally arrives(!), will be the only true Bluetooth LE streaming protocol and hopefully make the split MFi/ASHA world go away… I wouldn’t hold my breath, though … See the thread LE Audio and the Future of Hearing, a.k.a., Waiting for Godot…, we’ve been waiting since 2020…