Firstly, you must have a 2.4G/5G dual band routers.
1. Make sure you have set the correct country code using raspi configuration.
select 'Localisation Options' and press 'ENTER'
select 'L4' and press 'ENTER'
select the correct country then press 'ENTER'
2. Use the 'iwlist channel' command to view the currently allowed frequency bands to be connected. These values are different for different countries.
3. Check the frequency band settings of your router 5G WIFI
For this router, only '149,153,157 or 161' channel can be selected if we want to use 5G WIFI, or can't find 5G wifi in Pi 4 SSID list.
4. Then you can find the 5G wifi on your raspberry pi SSID list