Code M tells the IRS you made the "Mail in election".
In which case, you are required to mail the transaction details to the IRS within three business days of IRS accepting your tax return. the description "see Stmnt" refers to that document.
If you are mailing in your federal tax return, you can attach the statement at that time.
If you select "various" for date Acquired, the word "various" will appear (should appear) on Form 8949.
If you select "various" for Date Disposed,
then TurboTax apparently (and correctly) expects transaction detail to follow.
