Cracks in the window lintel/clinker - How to act?

Hello everyone,

we recently purchased a single-family house and will soon have some old windows replaced.
We have noticed cracks in the window lintel. It is on the west side of the house. Year of construction 1989. Apparently, the lintel of one window has sagged.

What could be the reason for this? What would be the best approach here? Leave it as it is for now? Can we do something ourselves? Simply seal the joints?

The images are no good (detail zoom instead of context); the inside is completely missing.

The pictures are useless like this (detail zoom instead of context); the inside is completely missing.

Excuse me? Which inside? You want an overall view of the house side?

Excuse me? Which inside surface?
You want an overall view of the house side?

On the one hand, you need the allocation of the offset within the clinker facade including the surroundings to erode a possible cause,
and on the other hand, of course, the interior view of the masonry, how the whole thing might also appear inside.
(By the way, the photos are not displayed for me at all. This is usually due to incorrect use of the attachment option here in the forum)

(By the way, the forums are not displayed at all for me. This is usually due to incorrect use of the attachment feature here in the forum)

I see the images, both on mobile and desktop alike, but without context they simply tell nothing. Quick click.

I will try to obtain more pictures.