is there a plug and play external antenna for Sagemcom Fast 5688W Gateway

Thanks I will look into it. Otherwise, The only way to improve signal  between tower and sagecom without disassembling the device is an expensive amplifier that will amplify band 71,as well as the others in the 600mhz range is the WilsonPro 710i or the Cel-Fi quatra 4000i products which may require a transmission agreement with T mobile since they do own the space. Haven't priced them nor know how to make them work.

For now I am also using Starlink as a backup usually at suppertime when the 5g signal seems to fail. When I got the 5g device, I thought I could cancel the $110/month Starlink, but I'll keep them both for now