I knew you weren’t going back there, so I’ve got someone else in the flat now.
Natasha enter a building in Budapest and heads upstairs to an apartment.
Shots of the interior entry way, the stairs, elevator and courtyard are all part of the Adria Palace in the northeast corner of Szabadság Square. The view outside the front doors is from the corner from the previous shot, as seen in the Street View below.
The Apartment scenes proper were shot on a soundstage, due in part to the explosions and cables need for the stunt work. When the chase continues up to the roof, that is a separate location as well.
(Black Widow, 2021)