I have similar inconveniences.
I have identified two problems, all values given - D/U [Mb/s]:
1) iPhone SE 2020 has noticeably worse wifi range than my previous iPhone 6s. In the place where 6s connects to my 5GHz network and still reaches 20/4, SE does not detect the network at all. The range on the 2.4GHz band is also worse and shows about one beam less. Sometimes, even close to the access point, a message is displayed saying that the network cannot be connected. This does not happen on any other device (4 iPhones, 2 iPads).
2) iPhone SE 2020 has a problem with the simultaneous use of the 2.4GHz band over wifi and bluetooth. When I turn off bluetooth, the bandwidth increases significantly. For example, near access point it increases from 29/44 to 98/82, far from access point it increases from 8/13 to 23/37.
I have already started regretting this purchase.
My setup is: Mikrotik hEX, UniFi AP-AC-LR