If you have Microsoft 365,

=LET(
    num_format, REPT("0", 6),
    count, 7,
    TOCOL(
        "A" & TEXT(SEQUENCE(count), num_format) &
            {"F", "B"}
    )
)

=TOCOL(TEXT(SEQUENCE(70000),"A000000")&{"F","B"})

You could use VBA:

Sub GenerateBarcodes()
    Dim i As Long
    Dim j As Long
    Dim ws As Worksheet
    Set ws = ThisWorkbook.Sheets(1)
    
    For i = 1 To 70000
        ws.Cells(2 * i - 1, 1).Value = "A" & Format(i, "000000") & "F"
        ws.Cells(2 * i, 1).Value = "A" & Format(i, "000000") & "B"
    Next i
End Sub

Or if you have Excel 365

=LET(
    seq, SEQUENCE(70000, 1, 1, 1),
    num, TEXT(seq, "000000"),
    F, "A" & num & "F",
    B, "A" & num & "B",
    VSTACK(F, B)
)

A more general version for E365 which can be easily used with any number of suffixes:

=LET(
    seq, SEQUENCE(70000, 1, 1, 1),
    num, TEXT(seq, "000000"),
    suffixes, {"F","B","C", any possible number of string or characters},
    rows, ROWS(seq),
    cols, COLUMNS(suffixes),
    total, rows * cols,
    result, MAKEARRAY(total, 1, LAMBDA(r,c, "A" & TEXT(INT((r-1)/cols)+1, "000000") & INDEX(suffixes, MOD(r-1, cols)+1))),
    result
)

With an older version of Excel, anter “A0000001F” in a cell, enter the formula below under it and drag down as far as needed:

=IF(
    RIGHT(B3,1)="F",
    LEFT(B3,7)&"B",
    "A"&TEXT(MID(B3,2,6)+1,"000000")&"F"
)