Hello Emilio, It's a pleasure to meet you; I'm Emilio from World 100 (We are neighbors 😃)

This is a super common question in my world, so let's answer it!

In Odoo V17.2, this feature already exists by default; you don't need to activate anything, but of course, you need to track absences with the Time Off App.

So, when you're assigning tasks to your team either from the Field Service app or Projects, a red badge (in the Gantt View) will appear, indicating that the task has some conflict.

Example:

If we click on that task, we'll identify, in this case, that Mitchell Admin will be absent on that day:

Similarly, you can find this warning in the Form View of the task:

You can also identify in gray color in the Gantt view the days when the company does not work (Based on Working Schedule) also Public Holidays.

I hope this answer helps you a lot!