This happened because DBeaver can't download driver via internet for some reason.

However you can install postgres driver manually by

1. Download postgres driver (postgresql-42.X.X.jar) file from https://jdbc.postgresql.org/download/
2. Put .JAR file into this Path (if there's no directory create it)

%APPDATA%\DBeaverData\drivers\maven\unknown\org.postgresql

3. Try to connect Connection again.