Allow the ability to connect to a HA database in the Add database connection box.
HostName=<host1, host2>;Port=<port number>;Database=<database name>;
For example (IBM DB2)
If your Db2 database is on server cube1 and cube 2, communicating through DBMS port 50000, and the database name is spatialdata, the connection string would be as follows:
Hostname=cube1, cube2;Port=50000;Database=spatialdata;
By specifying two IP addresses within the database connection string, ArcGIS Pro will attempt to connect to the first IP address. If it is unavailable, it will automatically failover to the second IP address. This should provide HA capabilities by ensuring a connection is established even if one of the database servers becomes inaccessible.