Here is a method using a Data Flow property as the control. Note, you cannot use a Run property with this method.
A boolean type Data Flow property ('Use_DB_Source') is defined.

The Data Flow property is referenced in the 'Enabled' property of the nodes in data source chains. In the upper chain the 'Use_DB_Source' property value is used to determine whether the nodes are enabled.

In the lower chain, the inverse of the 'Use_DB_Source' property value

The outputs of the two chains are attached to a Connection Point where the connection filter is configured so that the first enabled data set is connected to the output of the Connection Point.
Attached files
Load DB or Alternate - 23 Feb 2021.lna