The entrance to the project room at David B. Smith Gallery framed Sarah McKenzie’s Sentinel (Thyssen-Bornemisza Museum), 2021, a large canvas that, as its title implies, acted as a kind of watchman for this intimate space. The work depicts a museum guard’s empty stool standing next to a scrim-covered window, its louvred blinds casting their shadow ladder behind. On a perpendicular wall is an austere white painting—by Agnes Martin? Kazimir Malevich?—that hangs near a passageway, inviting a step that cannot be taken. McKenzie’s oblique portrayal of this famous Madrid institution at first glance