Here's a more comprehensive BYO Shorts-hiding extension which uses CSS instead of running JavaScript every time an element is added or removed anywhere in the DOM, and also supports the mobile version (CSS selectors are extracted from the https://soitis.dev/control-panel-for-youtube Hide Shorts feature)

https://gist.github.com/insin/ef93c7d87b1f97f1c9411e6128d520...