VirtualBox 6 will install NDIS6 driver as default. You need to install NDIS5 as docker need to work. After you download latest VirtualBox from official site, run following command in command prompt to let installer install NDIS5 driver.
VirtualBox-6.0.4-128413-Win.exe -msiparams NETWORKTYPE=NDIS5
This command will install NDIS5 driver and you will have docker work again.