This is a known issue with Roku TVs. It happens both with WiFi and Ethernet. When you turn the TV on it can take 5 or more minutes before it connects to the network. Roku is likely trying to resolve specific Public IP addresses to determine if you are connected to the Internet and if they are not available, timeout or are slow to respond it will take longer to connect. They are also likely performing a speed test before it reports you are connected.
I have been dealing with this same issue for years, across multiple model TV's and standalone devices. Roku does not seem to think this is an issue.
I have found if I open an app it will warn me there's no network connection. If I select "Continue Anyway", the app opens and works as normal. This always works with my local network apps, PLEX and TABLO, and sometimes works with streaming apps like PLUTO and NETFLIX)
