Not saying this is it, but I never managed to block YouTube shorts with brave adblocker (in mobile), where I can do it with ublock. If you can do it, please explain, I promise I will try asap (I really dislike ff mobile UI).

On mobile (similar on Desktop), just go to Setting -> Shields and Privacy -> Content Filters.

In there are a bunch of Youtube related blockers (including Shorts), that I find work really well. Mobile Brave also lets you lock/screen off your phone while a YT video continues playing, which is a killer feature for listening to podcasts.

I found myself becoming addicted to YT Shorts, and Brave's filters totally solved my problem.