Mercury’s best appearance of 2021 occurs during May. The planet is visible in the west-northwest above Venus. The appearance begins during late April. On May 28, the apparition ends with a close Venus – Mercury conjunction, the closest easily visible until 2033. About 30 Venus – Mercury conjunctions occur during the interval, but some close groupings are lost in the sun’s glare.
This episode is also available as a blog post: https://whenthecurveslineup.com/2021/04/25/2021-may-years-best-mercury-evening-appearance/