Sage Advice : Equipment
Does heavy armor reduce Dexterity saving throws or ability checks other than Stealth?
If you have proficiency with it, heavy armor doesn’t affect Dexterity saving throws or ability checks, other than Stealth.
If you attack with a shield—most likely as an improvised weapon—do you keep the +2 bonus to AC?
Attacking with a shield doesn’t deprive you of the shield’s bonus to AC.
Written by Jeremy Crawford (Sage Advice Compendium v2.2)