If the SSIDs are the same (between 5 & 6 GHz), a client may automatically switch to the 6GHz band if it offers better signal strength/performance. However this is subject to device settings and "nuances". A device-configured preferred band may commonly take priority, guiding the device to connect to the specified band if it is available and performing well. Those AP suggestions and band steering messages do influence the device's connection decisions, especially when the device-level preferred band is set to "No Preference" or when the preferred band is not performing optimally. So...with Windows client settings, don't forget those "Preferred Band" driver settings.
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