from arcgis.gis import GIS
from arcgis.mapping import WebMap
gis = GIS('pro')# if running this from Notebook for ArcGIS in AGOL/Enterprise, replace this line with gis = GIS('home')
wmItemId = "" #put the id of the webmap in here
wmItem = gis.content.get(wmItemId)
wm = WebMap(wmItem)
for lyr in wm.layers:
I wrote that to be run from the Python window in Pro, but see my note in line 3 about using it in ArcGIS Notebook. Just put the ID of the web map item into line 4 and it should print out all the layers for the given webmap.