Is it possible to make one calendar for all resources?

Yes. Let's look at the example of generic holidays schedule. Create a rule for holidays.

In this rule, set up a calendar with the desired schedule.

In the calendar settings, click on the menu icon. Then click Save schedule. Enter a name and save it.

After that, this calendar will appear in the list of shared calendars. Open the calendar settings of another resource and click on the menu icon. Select the desired calendar from the list.

This way you can create shared calendars. If you change the schedule in the shared calendar of one resource, the schedule will be updated in all resources where this calendar is used.

If you need to update the schedule in only one resource that uses a shared calendar, then first detach the calendar from the work rule.

To do this, open the calendar settings and click on the menu icon. Then select Schedule for this rule only.

After that, change the schedule in the calendar. This time, the schedule is not changed in other resources.

To delete a calendar, make sure that it is not used in any resource rules. Otherwise, you will not be able to delete the calendar.

Open the calendar settings rules. And click on the menu icon.

Then click on the menu icon of the calendar you want to delete.

Delete the calendar.