I too had the same issue after I bought my new MBA M1 2020. I transferred all the data from my MBA 2012. Initially when I got my M1 during the initial setup I think my wifi worked fine. But once I transferred all my data to the new one, it started showing this issue. WiFi is always connected and green in Network Settings but not actually connected to the web. I tried with customer care and was finally advised to take it to a Genius. Anyway after a long days searching, found this link. macreports.com/how-to-reset-network-settings-on-mac/ but the catch is, this one too is works just once. In the next shut down and boot, WiFi issue resurfaces again.