you can add to the database_url: ?ssl=true&sslmode=require (pick the mode you actually require)
if your server supports tls1.3+ you should force 1.2 on the client:
FUSIONAUTH_APP_ADDITIONAL_JAVA_ARGS="-Djdk.tls.client.protocols=TLSv1.2"
(https://fusionauth.io/community/forum/topic/938/secure-db-connection-with-tls-1-3/4?_=1629097757303)