iMac wifi does not connect to internet

After 5 years of flawless performance, all of a sudden, I cannot get internet over the wifi on my iMac. Other devices have no problem, so it is not a router or internet issue.

I can access the internet with an ethernet cable to the same router I was connected to by wifi.

Yes, I have restarted the iMac and router per the articles, but still not working.