Thibaultmol Would it be possible to at least get the 80%? That'd be much better than nothing at all. As long as it's transparently communicated to the user that this is a best-effort filter rather than a definite one, I think it'd be fine.
Another proxy that could be used to filter shorts would be, well, the length. I typically do not ever want to see a video that is <1 minute and I usually even want >4 minutes. The current user-exposed filters are not able to model any such filter. Improving those would go a long way towards enabling users to sort out the rubbish themselves.
I also had a look at what metadata YT reports in its HTML <head>. For shorts, it has the /shorts/ URL in the attribute of the following tags:
<link rel="canonical" href="https://www.youtube.com/shorts/jknHjBSIk7c">
<link rel="alternate" type="application/json+oembed" …>
<link rel="alternate" type="text/xml+oembed" …>
<meta property="og:url" content="https://www.youtube.com/shorts/jknHjBSIk7c">
<meta name="twitter:url" content="https://www.youtube.com/shorts/jknHjBSIk7c">
<meta name="twitter:app:url:googleplay" content="https://www.youtube.com/shorts/jknHjBSIk7c">
I have never worked with search indices but perhaps some of those metadata are available to you?