I have been able to somewhat reasonably block youtube shorts with the following custom filter ublock origin rules (on firefox at least). Note that it might accidentally hide some legitimate stuff but from my experience it should be pretty minimal if any. I think to hide the shorts from the left sidebar it hides one of your subscribed channels but that's all I've noticed so far.

www.youtube.com##ytd-rich-section-renderer.ytd-rich-grid-renderer.style-scope:nth-of-type(1) www.youtube.com##ytd-rich-section-renderer.ytd-rich-grid-renderer.style-scope:nth-of-type(2) www.youtube.com##ytd-rich-section-renderer.ytd-rich-grid-renderer.style-scope:nth-of-type(4) www.youtube.com##ytd-guide-entry-renderer.ytd-guide-section-renderer.style-scope:nth-of-type(2)