Try moving your Roku around a little - at the frequencies used by wifi, even a couple of inches can make a big difference sometimes.
Sometimes Roku wifi connections can be improved by setting them up from scratch again. See if this procedure helps any:
Restart your router (even if other devices have no problem finding and connecting).
After the router comes back up, restart the Roku via Settings > System > System restart (for a Roku TV it's Settings > System > Power > System restart) to start with a clean slate.
Find and connect to your network via Settings> Network > Set up connection
Roku Community Streaming Expert
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Streaming Stick 4K+ 3821 | Streaming Stick+ 3810 | TCL Roku TV 43S245/C107X