"If an employer adopts a plan during the employer's 2021 taxable year (but not later than the due date, including extensions, for filing the employer's 2020 tax return) and elects to treat the plan as having been adopted as of the last day of the employer's 2020 taxable year, then the plan sponsor will not be required to file a Form 5500 with respect to the plan for the plan year that begins during the employer's 2020 taxable year (references to Form 5500 include the Form 5500-SF and Form 5500-EZ unless otherwise noted).

"Instead, the first Form 5500 required to be filed with respect to the plan will be the 2021 Form 5500. However, the plan sponsor will be required to check a box on the 2021 Form 5500 indicating that the employer elects to treat the plan as retroactively adopted as of the last day of the employer's 2020 taxable year....

"[IRS anticipates] that similar rules will apply to the retroactive adoption of a plan pursuant to section 201 of the SECURE Act after an employer's 2021 taxable year." [IRS Employee Plans News, Aug. 6, 2021]