First thing to do is check the hardware of the RokuTV. From the Home Screen, go to Settings/Network/About and see if you have a MAC address listed. If your MAC address (not your IP address) is all zeros 00:00:00:00:00:00, then indicates a problem with the network card/wifi module in the RokuTV. If your MAC address is fine, then try connecting to a mobile hotpot if available to you. If able to connect to a mobile hotspot, then wireless capability is working fine and the issue is likely your network setup. A further test would be to connect your RokuTV via ethernet cable if your RokuTV is so equipped. Thus, if hotspot and ethernet work for you, then just need to tinker with network settings to make sure optimized/compatible with Roku devices. (wifi connection).
Feel free to post back with RokuTV model number, router model number, and ISP (internet service provider) and hopefully can tailor/narrow down some suggestions for you.
In the alternative, you may try experimenting with the Fast Start setting of the RokuTV. Some find keeping Fast enabled minimizes network disconnects, while the opposite is true for others. (when Fast Start is enabled, it may not detect a network disruption and requires a system restart to reconnect). The Fast Start feature is located under Settings/System/Power/Fast TV Start/[Enable] or [Disable].
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102