Can be any case as long as the recusal announcement is made after market creation on February 28th.

Recusals happen for a number of different reasons. For example if the justice had previously presided over a case in a lower court. Just last October Clarence Thomas recused himself from a case the court didn't even grant certiorari, and since the justices are not obliged to explain why they recuse it can be surmised that he did it for PR purposes to rebut future calls for him to recuse himself from January 6th related cases due to his wife's support for Trump at the time.

There do not appear to be any circumstances that require a justice to recuse even when there is an apparent conflict.