I believe you are correct. Must be at least 2 years between sales on which you can claim the exclusion.

 I believe you can Choose which home you wish to claim the exclusion for, as it seems (without looking at the form) that the question is worded something like "Do you wish to claim the exclusion ...."

Figure which is most advantageous and claim it on that year, - or delay the 2022 sale (if the gain is a significant tax cost.)  They need to remember that in lot's of the country the Real Estate market is hot right now, and may not stay that way if they delay the 2nd sale another year, and market conditions may cost more than the tax. - Or it could keep going up, Who Knows?