How to remove a reflection from shooting through a window?!!!?

Also after the fact, a polarizing filter on your camera would probably help.

Just a small aside, following from what you said, that you own the rights because you took the photo. In fact, especially but not only in France, you and a building owner often share the rights. For example, you need permission to share a picture of the Eiffel Tower at night. Typically, buildings over 120 years old are OK, but the Eiffel Tower lights are a recent addition. So your photo is OK, I think, but you need to look closely at each photo of buildings, just as you have to look closely at each photo of people and get a release from each one.

This is a minefield for the professional photographer, and if you are one, or planning on heading that way it's as well to be on top of it. Opinions differ as well on what laws actually mean and how to apply them! Here are guidelines for people planning on submitting building pictures to Adobe's Stock Photo service. Property release and protection guidelines for Adobe Stock  . Rules for editorial purposes (eg news stories) may be different.

Also Known image restrictions (lists some well known buildings with particular rules and/or laws). Did you know that while most cityscapes are OK, Las Vegas is not? That you can publish photos of the Statue of Liberty, but not of replicas? And you can't include Brasilia Cathedral or the Walt Disney Concert Hall in any commercial shot...?

In my opinion

Select the patch tool areas like this

After

Then create a new layer with 50% gray fill and change the blending mode to soft light

then dodge and burn with no more than 20% of exposure

something like this

If you dedicate more time, you will have a better result than me

I hope that helps,

I would start by making a mask of the sky, which is easy since there's nice clear separation. I would fix the sky by adding gradients set to Darker Color, working top to bottom.

I would then add a Levels adjustment, masking out the sky, and  then adding the edges where the reflection is with a black-to-white gradient set to multiply mode, and adjust the mid tones so they match. The right edge of the reflection is a little brighter that the rest, so you could either try finessing the mask, or add another adjustment, which would probably be easier.

Finally, I would add a curves adjustment layer, to punch up the contrast in the three-quarter tones.

Quick try (Mask still needs work):

Hi

Just a thought, you can find (similar) photos of Mont-Saint-Michel on (exemple) File:L'abbaye du Mont-Saint-Michel.JPG - Wikimedia Commons

Pierre

I've edited pics like that at work sometimes and what I used to do is isolate that area, copy that onto another layer, set that layer to Multiply and tweaked the opacity until it starts to match the rest of the background.  It may not be the best solution though.