The still image of the video shows that water has penetrated the basement. The interior plaster of the walls has detached from the masonry, efflorescence and salinization cause the mortar structure of the interior plaster to dissolve.
Rust on metal parts, rot on wooden windows and doors, mold, and spores in
the cellar and first-floor area are the result of moisture penetrating from the
outside.
The high humidity in the basement penetrates all surrounding walls and
ceilings and thus also reaches the living rooms on the first floor.
Basement and first-floor stairs are made of wood and have direct contact
with the humid air of the basement.
All structural parts of the stairs, as well as the wooden interior doors
and floorboards on all floors, are so weakened by woodworm infestation that
they have to be replaced.