“Twenty Years of Painting: 2001–2021” was the first show of Francesco Clemente’s work in Los Angeles in almost two decades. (The artist’s last outing, an elegiac 2003 Gagosian presentation that spanned New York and LA, offered a selection of then-recent works that conspicuously absented the human figure—a resonant meditation on loss.) Here, in a decommissioned and vacated Depression-era post office in Santa Monica, thirty pieces were spread across some fifteen thousand square feet of exhibition space.