As noted by MacRumors contributor Steve Moser, and confirmed by Aaron Zollo, the iPhone 12 lineup introduces support for Personal Hotspot tethering over faster 5GHz Wi-Fi, compared to 2.4GHz Wi-Fi on previous iPhones.
Personal Hotspot over 5GHz Wi-Fi is enabled by default on all iPhone 12 models. In the Settings > Personal Hotspot menu on these devices, there is a new "Maximize Compatibility" toggle that reverts Personal Hotspot to 2.4GHz Wi-Fi when enabled, with Apple noting that this may reduce internet performance on devices that are connected to the hotspot.
The combination of iPhone 12 models supporting higher-speed 5G networks and 5GHz Wi-Fi's higher maximum throughput paves the way for faster Personal Hotspot, but testing will have to be done to confirm the exact speed improvements. Keep in mind that while 5GHz Wi-Fi is faster than 2.4GHz Wi-Fi, it has shorter range, so Personal Hotspot speeds will vary based on the distance of a tethered device to the iPhone.
Personal Hotspot allows an iPhone's cellular data connection to be shared with other devices like a Mac over Wi-Fi, Bluetooth, or Lightning.