Guest network almost entirely on 2.4g?

I have 6 visitors today and tried out the guest network for the first time. It seems that almost all the devices of my guests can only connect to the 2.4g band throughout the day. Is this by design? The guests are friends of my daughter. While her iPhone steadily connect to the 5g band (she's on the main network) most of her friends (on the guest network) can only connect to 2.4g.