Re: Birthday email flow matching any date instead of just month and day MM/dd
@BHarTT
Try this:

SharePoint stores dates internally as yyyy-MM-dd
I noted that you have almost 5000 items in the list - Flow can't retrieve more than 5000 items unless you have a premium license.
It would be better if you added two additional columns to the list - one for the month and another for the day of the birthday. Do not make them calculated columns - have a Flow populate the new columns. If you do so, then you can use an OData filter query which would be much more efficient.
I tried solving your issue using substringof and endswith in an OData filter but was not successful.