zoneinfo

PEP-615 (landed in Python 3.9) introduced the module zoneinfo. The module provides access to information about time zones. It will try to use the information about time zones provided by the OS. If not available, it falls back to the official Python tzdata package which you need to install separately.

from zoneinfo import ZoneInfo
from datetime import datetime

ams = ZoneInfo('Europe/Amsterdam')
dt = datetime(2015, 10, 21, 13, 40, tzinfo=ams)
dt
# datetime(2015, 10, 21, 13, 40, tzinfo=ZoneInfo(key='Europe/Amsterdam'))

la = ZoneInfo('America/Los_Angeles')
dt.astimezone(la)
# datetime(2015, 10, 21, 4, 40, tzinfo=ZoneInfo(key='America/Los_Angeles'))

You should not use pytz anymore.