I'm an older guy with little, to no technical experience.  But in setting up my eero network and SMART devices, I ran into the 5.0/2.4 GHz issue.  I was astonished to find that I had to ask for eero's permission basically each time I ran into this issue.  That happened again this morning when after getting my first I-phone, I tried to set up my Rainbird nine process.  First, eero makes it seem easy to call and they will flip a switch, and it's done.  Not if they're closed. I've now been on hold for approx 30 minutes and getting really tired of hearing my call will be answered in the order it was received.  I wonder how many people are calling support right now to have their 5.0 GHz network shut down so they can add a 2.4 GHz device?  How many people have to complain before eero concedes this is an issue.  I just hung up as I had no more time to wait to accomplish such a simple task. eero, get some business sense!  Listen to you customers.  Quit making excuses for your OBVIOUS shortcomings that are despised by the people who have paid your was to success.  FIX THE DAMN ISSUE!

Strange. I have 3 Eeros (not Pro), one on each level, and my old Kindle, old laptop, old Firestick, and several IoT devices all joined right up on 2.4g without issue plus all the newer stuff that does 5G.  My only problem is in configuring new IoT devices which are on 2.4g but my phone is on 5g (and can't be forced to 2.4g) so the configuration Apps can't find the devices. i suspect the issue for you might not be the band, but the fact that the Eero's require a modern security protocol and if the device can't use that, then it isn't going to work on 2.4g or 5g ... I have one really really old device in that boat ... I had to keep my old router plugged into the Eero and use a different SSID just for that one device.

I have a Kasa smart plug, less than six months old. I have paused 5G but still won't work Alexa can no longer control my plugs. I wasn't expecting issues like this. My Spectrum supplied router had no such issues. Can this not be fixed? I don't want to deal with this every time the power blinks and resets every device on line.