Formula to Account for Weekend Days for an SLA

I have just tested the formula using the sample spreadsheet you uploaded and all calculations for a Friday to Monday situation showed 2 which is as you'd expect i.e. two working days from the Friday to the following Monday. I cannot replicate the example you give where you got a Friday to Monday being 1 - perhaps upload the 'problem' spreadsheet (or appropriate part) for us to review.

In the above you show 2023 dates but all dates in the example were 2024 so I'm guessing you are testing on a different sheet.