Maximum number of IntelliJ Run Configurations before they roll off

You can open Run | Edit Configurations and check Share checkbox for those configurations you want to save. And those will no be deleted.

Or, if you don't want it to be shared, you can click Save icon in the same configuration window. This configuration will also not be deleted.

You can find more information here

I know this is an old post but I got the same issue and managed to find out how to set the limit.

From IntelliJ documentation:

By default, 5 temporary configurations are allowed per project. You can change this limit via the Edit Configurations dialog.

Link to documentation on how to change the limit.