I have tried to add all IP addresses listed, but didn't work.

The updated documentation now states:

IP addresses

• 142.251.74.0/23
• 2001:4860:4807::/48 (Optional, for platforms that support IPv6)

If you're connecting to a Cloud SQL PostgreSQL instance, you'll need to add the listed IPs to the authorized networks list.

https://support.google.com/looker-studio/answer/7288010?hl=en# -- under "IP Addresses"