That tool doesn't support geoprocessing environment settings, but try
Project, Options, Geoprocessing ... Add outputs to an open map
Is it toggle on?, if so, try toggling it off.
'memory' workspace is another option to try
Write geoprocessing output to memory—ArcGIS Pro | Documentation
or at the end of your script, you can add another select layer by attribute with the clear selection option
Delete is generally the recommended approach, but it shouldn't take that long, unless you are working with non-locally stored data
... sort of retired...