Cannot get iMac to connect to Wi-Fi

Welcome to Apple Support Community.

First, review Connect to the internet with your Mac - Apple Support to make sure those settings are correct. Then, take a look at: If your Mac doesn't connect to the Internet over Wi-Fi - Apple Support. I'd also suggest that you read: Recommended settings for Wi-Fi routers and access points - Apple Support.

If the issue persists, add a new Wi-Fi network location and test: How to use network locations on your Mac - Apple Support.

If Wi-Fi still isn't working right, Start up your Mac in safe mode - Apple Support and test there. Also, Use Apple Diagnostics to test your Mac - Apple Support and see if any issues are flagged.

Cheers,

Jack

Please follow the steps per Apple's instructions in If your Mac isn't connecting to the internet over Wi-Fi - Apple Support