Is the DMG’s Disarm option an entire action, or a replacement for a single weapon attack?


My confusion comes from the somewhat ambiguous wording of the Disarm action as described in the Dungeon Master’s Guide (p. 271):

A creature can use a weapon attack to knock a weapon or another item from a target’s grasp. The attacker makes an attack roll contested by the target’s Strength (Athletics) check or Dexterity (Acrobatics) check. If the attacker wins the contest, the attack causes no damage or other ill effect, but the defender drops the item.

Two things stand out to me:

A creature can use a weapon attack

One way to interpret this is to mean that this is replacing a normal weapon attack, disarming the target instead of dealing damage. The other way to interpret this is that this weapon attack is special; that despite being called an attack, it’s intended to be its own action type.

If the attacker wins the contest, the attack causes no damage or other ill effect

This also stands out to me. If this were its own action, and not a replacement for a regular attack, then it wouldn’t be necessary to specify that damage is negated; it would simply be presumed to deal no damage.

What is the correct way to interpret this action? Is it its own action, or a replacement for a single attack as part of the Attack action? If a character gets the Extra Attack feature, can Disarm replace every attack they’re otherwise allowed to make?