Workdays in current Month

Ahh, to be honest, I'd strongly recommend updating it or asking your admins to because that's crazy.

But if you can't then another way to do this (although I'm not the biggest fan of this), is to make a day column in Power Query (really simple to do - just select the date field in your calender table, then fo to add columns tab at the top, select the dates dropdown on the top right and then select Day).

^This will add a Day field to the calender table like Monday, Tuesday, etc..

Then in Power Query, make a conditional column and then say If Monday, then Weekday, If Tuesday, then Weekday, etc...

Then in your model, make sure that you do it in a way where you link the calendar table to any dates fields in other tables and then you'll be able to use that column as a filter in your pages.

Hope that makes sense.