One date slicer for multiple date columns

The fundamental issue is that you don't want to have multiple possible filtering paths from one table to another since this creates model ambiguity.

For example, if following relationship paths, Dates filters SentEmails and SentEmails filters EmailEvents, then having Dates directly filter EmailEvents via a relationship introduces ambiguity, which is why Power BI sets these relationships to be inactive.

There's no simple fix to create a good data model. The resolution is to structure your model to avoid bidirectional relationships when possible and avoid relationships directly between fact tables wherever possible.

Further reading:
https://www.sqlbi.com/articles/bidirectional-relationships-and-ambiguity-in-dax/

https://www.sqlbi.com/articles/syncing-slicers-in-power-bi/

https://www.sqlbi.com/articles/different-options-to-model-many-to-many-relationships-in-power-bi-and-tabular/