The best option, in my opinion, is to create a custom column with two values:
If the type is Pandemic, the term "pandemic" is used. If the type isn't pandemic, it's called non-pandemic.
As a hierarchical slicer, you'd utilize this new column + Absence Type.
This would allow the user to choose between the following options:
- Select all (If the user deselects everything a select all will also be applied)
- Non pandemic only
- Pandemic only
- Any one or more types of absence