I took a first stab at this and it seems to be working fine. Further testing would be needed though - It would be amazing if someone could take a look.
archnode → made their first commit to this issue’s fork.
I had the same issue with dompdf running Drupal in a docker container behind a proxy.
As the original server can't access the external base url, linked assets (css, images) can't be resolved by drupal internally. I solved this by mapping the external domain to localhost in the container, but one could also add absolute paths to the local webserver (e.g. http://127.0.0.1).
With the default date set to 'now' this happens e.g. today: week 13, 27th march 2023 and displays the calendar default starting with 1st april 2023 to 7th april 2023.
Thank you for taking the time to respond. Please tell if you need anything else.
archnode → created an issue.