You are incorrect. If a device is 2.4 ghz, that's all it will see. You can have 5 and 6 ghz with the same ssid and wpa key, and it will not interfere with the 2.4 in any way, because a 2.4 ghz device cannot see anything BUT 2.4. I have an raxe300 Netgear wifi 6 router and my 2.4 ghz older tv works just fine as does other other devices like BLINK cameras/doorbell and other devices, like my inside ring camera.
You can tell your phone to use 2.4, each phone is different in how it's done.
Per MYQ -
Does myQ only work with 2.4 GHz?
If your router has both 2.4 GHz and 5 GHz bands, ensure 2.4 is GHz enabled. myQ Wi-Fi products only support 2.4 GHz band Wi-Fi and will not connect to 5 GHz band Wi-Fi.
Anyone else who has told you otherwise, is misinformed. My credentials, I am a network engineer with multiple certifications. If there is a question about my knowledge, ask TiffanyR or LisaH.