It may be the case that this is indeed specific to geodatabase 'folders' and not folders in general.
But strangely... it doesn't matter to PRO's arcpy so it sounds like it is a Catalog issue then
import arcpy
pth = r"c:\Data\Pro_base.gdb"
arcpy.env.workspace = pth
arcpy.ListFeatureClasses()
Out[21]: ['Carp_5x5km', 'Carp_5x5km_label', 'xy', 'mesh_sample', 'connecttoline', 'xy1000', 'small', 'xy1000_closest1', 'Line', 'Points', 'PointsOnLine', 'Curve', 'PointsOnCurve', 'connecttocurve']
pth2 = r"c:\Data\Pro_base.GDB"
arcpy.env.workspace = pth2
arcpy.ListFeatureClasses()
Out[24]: ['Carp_5x5km', 'Carp_5x5km_label', 'xy', 'mesh_sample', 'connecttoline', 'xy1000', 'small', 'xy1000_closest1', 'Line', 'Points', 'PointsOnLine', 'Curve', 'PointsOnCurve', 'connecttocurve']
pth == pth2
Out[25]: False
os.path.exists(pth)
Out[26]: True
os.path.exists(pth2)
Out[27]: True