Um… I’m not sure what vendor is telling you that a client works better on 2.4 GHz rather than 5 GHz but I find that hard to believe…
either way, you should always separate your bands into a separate 2.4 GHz and 5 GHz SSID as it’s the only way to ensure that 5 GHz clients use 5 GHz.
Id create a separate SSID that is only broadcast on 2.4 GHz and one that is only broadcast on 5 GHz. 5 GHz should always be better as there should be less utilisation on those channels.
Please feel free to hit that kudos button