Even if your client might consider someone else’s advice that an annual report and information return might not be required, your client might consider filing a Form 5500 return desirable because the IRS counts a plan trust’s Federal income tax statute of limitations from that filing.
IRS Announcement 2007-63, 2007-30 Internal Revenue Bulletin (July 23, 2007).
https://www.irs.gov/irb/2007-30_IRB#ANN-2007-63
When the plan’s administrator files its Form 5500 for 2020, three years later (and, often, practically sooner) 2020 will roll out of the years the IRS would examine.
Although an employer might feel there is little risk that the IRS would find an operational defect for 2020, why would an employer/administrator leave open any possibility of being put to the burden of responding to IRS information requests (if it is inexpensive to file the 2020 Form 5500)?