When using arcpy.SelectLayerByAttribute() in ArcGIS Pro 2.6.X, all records are returned instead of just the selected records inside both the IDE and the ArcGIS Pro user interface.

Solución alternativa

Options:

1. Use arcpy.management.MakeFeatureLayer first before arcpy.management.SelectLayerByAttribute.
2. Connect to the feature through the path to the project.
3. Use the python window or Notebook within the ArcGIS Pro 2.5.1 User Interface

Example for option 1:

import arcpy

arcpy.management.MakeFeatureLayer(r"C:\Users\Desktop\Shapefile\Arcpy\esri\Testing.gdb\Polygons","Testl")

arcpy.management.SelectLayerByAttribute("Testl", "SUBSET_SELECTION", "LANDAREACODE = '021'", None)

print(arcpy.management.GetCount("Testl"))

Example for option 2:

import arcpy

import os

aprx = arcpy.mp.ArcGISProject(r"C:\ArcPy\ArcPy.aprx")

maps = aprx.listMaps()[0]

Polygon = maps.listLayers()[0]

print(Polygon)

arcpy.management.SelectLayerByAttribute(Polygon, "SUBSET_SELECTION", "LANDAREACODE = '021'", None)

print(arcpy.management.GetCount(Polygon))

Example for option 3:

import arcpy

arcpy.env.workspace = r"C:\Users\Desktop\Shapefile\Arcpy\esri\Testing.gdb"

a=arcpy.management.SelectLayerByAttribute("Polygons", "SUBSET_SELECTION", "LANDAREACODE = '021'", None)

print(arcpy.management.GetCount(a))

Pasos para reproducir