A Sonos Amp, or a Sonos CONNECT:AMP? The former does have a 5Ghz antenna and chipset, the latter does not, it was designed long before 5Ghz was economically viable. 

On all Sonos devices capable of commanding rear speakers (so the soundbars and the Amp) the 5Ghz antenna is reserved for use with the dedicated 5Ghz link tot the rear speakers - even if you do not use rear speakers. So while technically the option to use 5Ghz networks might be there, Sonos does not see a possibility to let you use it.

See Supported WiFi modes and security standards for Sonos products | Sonos

Yeah. The 5Ghz option is available on the other devices. I tried to connect all of them to it. But then the system failed to function properly. I could not install Google assistant since the AMP did not have the 5Ghz option. Isn't the amp able to connect to 5Ghz?

I bought it 2,5 years ago and it's the one when you search "AMP" on the sonos site. 

https://www.sonos.com/en-us/shop/amp

So I really don't know.

@Stefan71,

See here with regard to Sonos products and their WiFi network mode capabilities…

https://support.sonos.com/en-us/article/supported-wifi-modes-and-security-standards-for-sonos-products

That is a Sonos Amp, and not a CONNECT:AMP, so it should indeed have the 5Ghz capability in it. I’m not sure why you’re having trouble ‘seeing’ a 5Ghz connection on it. I would call Sonos Support directly to discuss it.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

The Sonos Amp cannot connect to 5GHz WiFi (see the link above from Ken), it uses its 5GHz radio exclusively to directly connect to surrounds and subs.