Photos very dark when uploaded

the browsers work with the s-RGB color profile – many photographers save their photos with adobe-RGB or ProPhoto RGB, sometimes even with 16bit per color channel.
When you upload these images to the media library, they are treated as if they were s-RGB images. Embedded color profiles are not taken into account in browser rendering.

Next: If you upload images from your professional digital camera without recalculating them for web use, most of them will be too large.
Wordpress will first convert them to a size of 2560px – and use this as the source for the other image format calculations. – It is therefore better to do the web optimization yourself in a program of your choice.

See a comparison : https://webers-testseite.de/image-comparison/

Allthough the ProPhoto RGB Color Room is much bigger than the sRGB – they will not be rendered in a correct way.

First try it with one photo that you have allready uploaded by which you notice the loss of quality described above (darker etc.)
Open the image in Photoshop, reduce it to a maximum width of 1500px, for example, and save it as sRGB. Upload this image and compare it with the existing library image. If the image is much better, you can do the same for the rest of your photos.

De rien. Comme je l’ai dit, ce n’est qu’une supposition, car cela m’est déjà arrivé. Je ne peux pas te dire si c’est lié. Mais cela vaut la peine de faire un test.