A reproducible example of ArcGIS API for Python issue Esri/arcgis-python-api#1769.

First create a virtual environment and install the dependencies from requirements.txt. (requirements.txt was compiled from pyproject.toml; if you prefer to use a tool to install the dependencies directly from pyproject.toml, it should yield the same results.) Then run the run_example.py script. The following steps work on Windows:

git clone https://github.com/skykasko/arcgis-python-api-date-example
cd arcgis-python-api-date-example
py -3.9 -m venv .venv
.venv\Scripts\activate
py -m pip install -r requirements.txt
py run_example.py

run_example.py will prompt you to enter a username and password to login to ArcGIS Online. (To skip this, edit lines 11 and 12 of run_example.py and enter the username and password directly in the code.) It then creates a hosted ArcGIS Online feature layer with a single feature based on the contents of layer_source.csv, which contains two different date values in two date fields. Finally, it attempts to update the date fields with two new, distinct date values.