Proficiencies
Do you gain proficiency in more saving throws when multiclassing? A class offers various starting proficiencies that you get if it is your first class. If the class isn’t your first, you get only the starting proficiencies listed for that class in the Multiclassing Proficiencies table (PH, 164). No saving throw proficiencies are included in that table. Regardless of whether a class is your first, you do gain any proficiencies that the class grants through its features. For instance, if you gain a level in cleric and choose the War Domain, you do benefit from the Bonus Proficiencies feature, even if cleric isn’t your first class.
Sage Advice Compendium, v2.7 r2021