Formula repeating LAMBDA/MAKEARRAY a result

Hecatonchire 

What is happening in 'Formula 2' is that the presence of the array in the IFERROR condition causes the result of CHOOSECOLS(Tab, 2) to broadcast to match the error argument in size.  I think the problem may be that CHOOSECOLS(Tab, 2) is still of TYPE 64 (array) despite it returning only one value.

Using '@' to truncate the supposed array may sort this problem

=LAMBDA(nbC, nbR,
    LET(
        Tab, MAKEARRAY(nbR, nbC, LAMBDA(r, c, c & "-" & r)),
        IFERROR(@CHOOSECOLS(Tab, 2), Tab)
    )
)(6, 1)