Is your feature request related to a problem? Please describe.
Maybe I forget I use a filter. I don't get a hint it is in use.
Describe the solution you'd like
Maybe add an alarming color-background circle to the filter icon, when it is in use.
There is a change it the opacity when a filter was set:
whithout filter:

with filter:

@nextcloud/designers Do you have a hint for me? I like it for exampe how it is done in the android deck app:

Desktop:
I don't know if it is accessible, but I question it's obvious.
If I already know this filter could be activated, yeah, it's a helpful fast check. So imo this would work for heavy users. But if I just wonder why I don't see all cards this wouldn't come into my focus.
We could also show some additional context to make it clear that the current view is filtered (if space allows) like trello shows the number of results:

Most helpful comment
There is a change it the opacity when a filter was set:

whithout filter:
with filter:

@nextcloud/designers Do you have a hint for me? I like it for exampe how it is done in the android deck app:
