Blazing Sunsteel

• WOTC Official Reminder Textofficial rules
  Equip — Equip [cost] ([cost]: Attach to target creature you control. Equip only as a sorcery.)

• WWizards of the Coast2020-11-10
  Official Ruling
  A creature can be dealt an amount of damage greater than its toughness. For example, if the equipped creature has 1 toughness and is dealt 3 damage, it deals 3 damage, not 1, to the chosen target.
• WWizards of the Coast2020-11-10
  Official Ruling
  If your life total is brought to 0 or less at the same time that the equipped creature is dealt damage, you lose the game before Blazing Sunsteel's middle ability goes on the stack.
• WWizards of the Coast2020-11-10
  Official Ruling
  Blazing Sunsteel is the source of the middle triggered ability, but the equipped creature is the source of the damage. For example, if the equipped creature is green, that ability can't target a permanent with protection from red, but it can target one with protection from green, though the damage would be prevented.
• WWizards of the Coast2020-11-10
  Official Ruling
  Opponents who have left the game aren't counted by Blazing Sunsteel's first ability.

Rulings via Scryfall