What does Wifi 6e limited compatibility mean?

I have the latest Xfinity gateway that has WiFi2.4, 5 and 6E. I use separate SSID’s because I want the ability to select which network to connect to.

I understand that combining the networks under the same SSID enables “steering” and in theory each device will connect to the best network but that isn’t always the case real-world, which is why I prefer separate SSID’s.

I understand that Apple recommends combining into a single SSID, as does Xfinity.

My question is, what “limited compatibilities” exist when SSID’s are not combined? Apple doesn’t explain in their support documents.

I get fantastic speeds connecting to 6E…1.5gb/sec.which is equal to my PC ethernet connection. I want to ensure I will always connect to 6E when within range and to my knowledge, if I combine and utilize steering there is no way to choose the 6E network to connect to.

Any input is appreciated. Thanks.