Michael
There are several videos on creating custom numbering schemes.
Check these out and see if one will work for you.  You might have to combine techniques but we're here to help if you hit a brick wall.

Sequential Numbers
Customer Codes
Sequential Annual Coding

Here is an example. I put the code in a button for testing but you could call the code in an event so you don't need to click a button.

Private Sub btnGenerate_Click()

    Dim D As Date, CurrentYear As Long, PrevYear As Long
    Static CaseNum As Long, CaseNumStr As String
    
    D = Date
    CurrentYear = Right(Year(D), 2)
    PrevYear = Nz(DMax("Mid(CaseNumber, 5, 2)", "CaseT"), 0)
    
    If CurrentYear = PrevYear Then
        CaseNum = Nz(DMax("Right(CaseNumber, 4)", "CaseT", "Mid(CaseNumber, 5, 2)=" & PrevYear), 0)
    Else
        CaseNum = Nz(DMax("Right(CaseNumber, 4)", "CaseT", "Mid(CaseNumber, 5, 2)=" & CurrentYear), 0)
    End If
    
    CaseNumStr = "ADA " & CurrentYear & "-" & Format(CaseNum + 1, "0000")

    If IsNull(CaseNumber) Or CaseNumber = "" Then
        CaseNumber = CaseNumStr
    End If

End Sub

You can test the change of year by setting D to a static year. For example. #15/8/2024#

Thank you for your assistance with this matter. I have looked at all of the video's that were suggested and reviewed the code provided by Kevin, however I am having issues with getting the functionality to work the way I am looking for. I am attempting to have to CaseNumber automatically fill as a user creates a new case with the Prefix remaining the same depending on the case type they are entering and the number format for example of XYZ-YYYY0001 then the next being XYZ-YYYY0002 and so further based on the year the case was started.

Kevin, thank you for your assistance with this matter. the general functions are working great, the only part that does not seem to be work is the case number increasing when I add a new record. Any suggestions would be greatly appreciated. I have tried the following:
If CurrentYear = PrevYear Then
        CaseNum = Nz(DMax("Right(CaseNumber, 4)", "ADACaseT", "Mid(CaseNumber, 5, 4)=" & PrevYear), 0) + 1
    Else
        CaseNum = Nz(DMax("Right(CaseNumber, 4)", "ADACaseT", "Mid(CaseNumber, 5, 4)=" & CurrentYear), 0) + 1
    End If

However it has not caused the case number to increase when a new case is created.