I received Form 1099-S and filed my 2019 taxes with Form 4797 line 1 blank (before I noticed the omission). I haven't heard anything from the IRS yet. I would think even if it was flagged, a quick manual review would show that the sum of all the 'gross sales price' entries add up to what should have been on line 1, so there was no underreporting. Don't have the software anymore but generally you can do quite a lot in 'Forms' mode, so I would think you could fill in line 1 manually that way.
