Mark a file that there is a comment (or a tag)

is there a way to see in the normal file view, that a file or folder has comments? or even tags? Currently I always have to open the details page to check it.

No, unfortunately not. There’s no setting in the Files app for a view with opened details.

At least an indicator (icon) would be helpful.

But you can file a feature request on GitHub:
(I haven’t found a request for that feature.)