I'm using some custom ublock origin filters that I found somewhere to block shorts across all of youtube:

!Youtube Shorts
www.youtube.com###guide-content #endpoint[title="Shorts"]:upward(ytd-guide-entry-renderer)
www.youtube.com###items #endpoint[title="Shorts"]:upward(ytd-mini-guide-entry-renderer)
www.youtube.com##ytd-browse #dismissible ytd-rich-grid-slim-media[is-short]:upward(ytd-rich-section-renderer)
www.youtube.com##ytd-browse ytd-grid-video-renderer:has(span.ytd-thumbnail-overlay-time-status-renderer[aria-label="Shorts"])
www.youtube.com##ytd-browse ytd-rich-item-renderer:has(span.ytd-thumbnail-overlay-time-status-renderer[aria-label="Shorts"])
www.youtube.com##ytd-search ytd-video-renderer:has(span.ytd-thumbnail-overlay-time-status-renderer[aria-label="Shorts"])
www.youtube.com##ytd-watch-next-secondary-results-renderer ytd-compact-video-renderer:has(span.ytd-thumbnail-overlay-time-status-renderer[aria-label="Shorts"])
www.youtube.com##ytd-browse[page-subtype="subscriptions"] ytd-video-renderer span.ytd-thumbnail-overlay-time-status-renderer[aria-label="Shorts"]:upward(ytd-item-section-renderer)
m.youtube.com##ytm-reel-shelf-renderer
m.youtube.com##ytm-pivot-bar-renderer div.pivot-shorts:upward(ytm-pivot-bar-item-renderer)
m.youtube.com##ytm-browse ytm-item-section-renderer ytm-video-with-context-renderer:has(ytm-thumbnail-overlay-time-status-renderer[data-style="SHORTS"])
m.youtube.com##ytm-browse ytm-item-section-renderer ytm-compact-video-renderer:has(ytm-thumbnail-overlay-time-status-renderer[data-style="SHORTS"])
m.youtube.com##ytm-search ytm-compact-video-renderer:has(ytm-thumbnail-overlay-time-status-renderer[data-style="SHORTS"])

Also separately, for blocking videos that don't exist yet, which I also dislike:

!Youtube upcoming videos
www.youtube.com##ytd-browse ytd-grid-video-renderer:has(ytd-thumbnail-overlay-time-status-renderer[overlay-style="UPCOMING"])
www.youtube.com##ytd-browse ytd-rich-item-renderer:has(ytd-thumbnail-overlay-time-status-renderer[overlay-style="UPCOMING"])
www.youtube.com##ytd-browse[page-subtype="subscriptions"] ytd-video-renderer ytd-thumbnail-overlay-time-status-renderer[overlay-style="UPCOMING"]:upward(ytd-item-section-renderer)