Taranika, Akroan Veteran

• WOTC Official Reminder Textofficial rules
  Vigilance — Attacking doesn't cause this creature to tap.

• WWizards of the Coast2020-01-24
  Official Ruling
  Untapping an attacking creature doesn't remove it from combat.
• WWizards of the Coast2020-01-24
  Official Ruling
  Taranika's triggered ability can target a creature that's already untapped. It still becomes 4/4 and gains indestructible.
• WWizards of the Coast2020-01-24
  Official Ruling
  Taranika's triggered ability isn't optional. If your only other creatures are bigger than 4/4, you'll have to shrink one for the turn.
• WWizards of the Coast2020-01-24
  Official Ruling
  Any effects that modify the target creature's power and/or toughness without setting them to a specific number or value will apply after its base power and toughness are set, regardless of the order in which those effects were created. The same is true of counters that modify its power and toughness.

Rulings via Scryfall