For example, the artificer's "Radiant Weapon" infusion gives +1 to attack and damage. Does it count as a magic weapon?
The Infuse Item feature states:
you gain the ability to imbue mundane items with certain magical infusions. The magic items you create with this feature are effectively prototypes of permanent items.
Additionally, the specific Radiant Weapon infusion says:
This magic weapon grants a +1 bonus to attack and damage rolls made with it.
(all emphases are added by me)