WiFi 6E capable Mac not staying connected to 6E?

Reporting the Wi-Fi 6E/5 problem here is not making Apple aware of it. You should send direct feedback to the appropriate Apple product team: MacBook Pro. Explain what you explained here.

Since you are attempting Universal control to devices that do not support 6E, and if you are providing a dual-band 5/6GHz SSID which you should do according to Apple for a 6E connection, then it stands to reason that it would switch to 5Ghz to access the devices on the other end of that Universal control connection. But let Apple tell you that if they respond to your feedback.

Kendall Cosby wrote:

This could be the source of the problem. My 2023 16" MacBook Pro (Ventura 13.6.4) would initially connect to the 6 Ghz WiFi 6E channel. But, then it would switch to the 5 Ghz channel.

 The cause of the problem turned out to be Universal Control.

 I have an iPad Pro (Gen 3, 17.3) and MacBook Air (2020, 14.3) that to do not have 6E support. When my MBP would establish a Universal Control connection with those devices, it would switch to the same 5 Ghz WiFi those devices are on.

After disabling Universal Control on my MBP, it stays connected to 6E.

OK.

If you upgrade to Sonoma 14.3 report back your findings at that time...

The current stable release of iOS including bug fixes, security updates PadOS 17.3,

Update your iPhone or iPad - Apple Support

The current stable release of Sonoma including bug fixes, security updates is macOS 14.3

Keep your Mac up to date - Apple Support

Keep your Mac up to date - Apple Support