By default, MainWP Google Analytics Extension supports GA4 properties, however, it is required to create Universal Analytics property also. To create GA4 property is a proper way so your MainWP Google Analytics Extension can connect to it, please do the following:

1. Go to the Admin panel
2. Click the Create Property button
3. After setting basic property info, click the Show Advanced Options link
4. Enable the Create a Universal Analytics property option
5. Proceed to finish the property creation process.