Rulings
Return to Dust can always target a second artifact or enchantment; it just won't exile it if it's not your main phase when you cast Return to Dust.
(wotc • 2021-03-19)
If a spell or ability copies Return to Dust, the copy exiles only the first target artifact or enchantment. This is because the copy wasn't cast at all.
(wotc • 2021-03-19)
Rulings
Return to Dust can always target a second artifact or enchantment; it just won't exile it if it's not your main phase when you cast Return to Dust.
(wotc • 2021-03-19)
If a spell or ability copies Return to Dust, the copy exiles only the first target artifact or enchantment. This is because the copy wasn't cast at all.
(wotc • 2021-03-19)