Democrats did not lose anywhere near 40–50 House seats in the 2022 midterms. In the 2020 election they held 222 seats; after the 2022 elections they held 213, a net loss of 9 seats, not 40–50. (en.wikipedia.org)

Although Sacks framed this as conditional on Biden continuing to let Bernie Sanders and Elizabeth Warren "dominate the agenda," we can still evaluate the measurable part of the prediction (the size of the House losses). Regardless of how one judges that policy condition, the forecasted outcome (40–50 lost seats) clearly did not occur, so the prediction is wrong.