Have had these drops right from the first beta of 14 all the way through to 14.3. the Drops only occur in spots where the Wifi signal is relatively weak (but used to work fine on iOS 13 and all previous versions). It’s only happening on my iPhone 11 Pro. It’s not happening on my iPad Pro when it’s in the same spot as the iPhone. That might just be because the iPad has better antennas than the iPhone.
The drops don’t occur when I’m right next to my router.
I have also tried it with other WiFi networks with the iPhone with the same results: when the signal is strong I don’t get drops, when the signal is weak I get drops every minute (again, in spots where it used to work fine on iOS 13)