Hide specific values in matrix

I don't think such an option is available in PowerBI (or at least, not in the default visuals). 
One possible workaround for this is to turn off the text wrap and auto-size width in the Column Header Options, and then manually resize the column until it's not visible. But the downside to this is that once a new week or column is added, you'll need to resize the column.

In the meanwhile, you can try to vote for ideas, such as this one: https://ideas.fabric.microsoft.com/ideas/idea/?ideaid=5f080970-9ddc-4d8b-8e51-8519eef2ce60 on the ideas forum.