Color profile not working in photos

My wife is a photographer. We setup Nextcloud as a replacement for Dropbox.

Problem is, Nextcloud is not respecting ICC color profiles. If we show photos in Nextcloud, the colors are dull and not managed, if you download the same file and display it, the color is perfect. So clearly the fault is with Nextcloud.

Problem is, I have seen people reporting this problem (2020 as an example) and no one even responded to him.

How do I fix this? I CANNOT use Nextcloud to demo photographs where the color is not correct. We are literally losing customers because of this problem.

I’m not a photographer, my cloud is for music producers - normaly DropBox Junkies as well and I feel with you!
I don’t know how to fix the problem either, but I could imagine that the ICC profiles are not included when generating the preview images, which are generated with loss for reasons of loading speed.
Have you already tried by completely disabling the preview image creation in config.php?

'enable_previews' => false,

The original images with the integrated ICC profiles would then be displayed in the browser and it then only the customer has to set the correct color profile handling in their browser.

Hope this helps,
much luck!