Date fields in Drupal 9 lack timezones and this is needed to allow events around the world to show local time accurately

I found the core issues about this problem.

[PP-1] Add ability to select a timezone for datetime field [#2632040] | Drupal.org

DateTimeIso8601::setDateTime() vs. DateTimeItem::schema(): (at least) one of them is broken [#2716891] | Drupal.org

Here’s the issue set aside for patches that can be applied with composer to fix the problem!

https://www.drupal.org/project/drupal/issues/3185750

Disappointed the fix isn’t (or maybe can’t be) in https://www.drupal.org/project/datetime_extras