Historical Rules · 24 September 2021
Rule 802.4
Official source text from the 24 September 2021 Rules release
If more than one player is being attacked or controls a planeswalker that’s being attacked, each defending player in APNAP order declares blockers as the declare blockers step begins. (See rule 101.4 and rule 509, “Declare Blockers Step.”) The first defending player declares all their blocks, then the second defending player, and so on.