Shorts can be hidden from YouTube with the following CSS and the Stylus browser extension (Firefox, Chrome). You can still access shorts on the channel page, but they will be hidden from subscriptions & home pages.
/* Shorts in subscription feed */
#items.ytd-grid-renderer
> ytd-grid-video-renderer.ytd-grid-renderer:has([href*="/shorts/"]) {
display: none;
}
/* Sidebar link to shorts */
[title*="Shorts"] {
display: none !important;
}
/* Dismissable shorts section on home page */
[is-shorts] {
display: none;
}