Hi Sam,
you could do something like this in the Python API (untested and written from memory, check the docs)
from arcgis.gis import GIS
from datetime import datetime
gis = GIS(.......)
items = gis.content.search("*")
for item in items:
d = datetime.fromtimestamp(item.modified/1000)
print(f"Item {item.title} was modified {d}")
Alternatively you can call the REST interface using the requests module in Python. I usually do a mix of both, but using RESTmore and more!
Regards
Carsten