Sorry, no, I was wrong.

The instructions to the form (pasted below) indicate that electronic filing may be available in 2022. So that means it might be available for 2021 returns. 

"What’s New
Electronic filing expected to be available in 2022.
Electronic filing of Form 5227 is expected to be available
2022, and the IRS will announce the specific date of
availability when the programming comes online."