Sounds to me like you are using Qlik Sense Cloud?
If that's the case then that file is managed through the hub as it's a file that you can use across apps. So the management of it is outside of the app.
If you go to your data files in the hub you can right click it and remove it
Hopefully this helps.
OK - so I had tried that and did not see that option.
I am using Firefox, and I do see a Firefox right-click pop-up.
Now that I know the Remove option should be there, seems like the browser's own pop-up is hiding Remove option. Good grief. Guess I need to see if IT policy will let me at least temporarily prevent the browser pop-up.
In case this ever helps anyone:
It turns out - the work-around is to press-and-release the Alt key. This makes Firefox's right-click menu disappear.
(I cannot find an option to prevent it from appearing in the first place. Add this to the list of web-app complications/annoyances... ;-)
A side note: A trash can icon would be consistent with the attached file removal approach and would avoid this problem altogether.