After migrating a fresh Raspbian install using the official 2020-04 Raspbian light image from my Raspberry Pi Model 2 to my new Raspberry Model 4, the Wifi was disabled at boot.
I tried configuring the Wifi using raspi-config but that didn’t change anything.
First, try rfkill unblock all and then reboot in order to check if the Wifi adapter is still unblocked after the reboot. In my case, this fixed the issue permanently and wifi worked immediately.
If that doesn’t help, check if country=... is set in /etc/wpa_supplicant/wpa_supplicant.conf. You need to set it to your correct country code to comply with regulatory limits. For example, use country=DE to set the regulatory domain to Germany.