Thank you. It works in Firefox, but only with my old style, which used to work by itself, but now it does not fix the number of columns on the main page.
Exactly:

#contents {
--ytd-rich-grid-items-per-row: 6 !important;
--ytd-rich-grid-posts-per-row: 6 !important;
--ytd-rich-grid-slim-items-per-row: 6 !important;
}

Well, it would not be bad to clean the thumbnail headers and make it possible to change the text of all three lines independently of each other. Something like that:

/* Remove the three vertical dots under the thumbnails and expand the description at the expense of the vacant space */
#button.ytd-menu-renderer,
#button > .ytd-menu-renderer.style-scope {
display: none !important; }
#meta.ytd-grid-video-renderer,
#meta.ytd-rich-grid-video-renderer,
#meta.ytd-rich-grid-media {
padding-right: 0px; }
/* On the main page - Remove the channel icon near the title under the thumbnail */
div#details.style-scope.ytd-rich-grid-media a#avatar-link.yt-simple-endpoint.style-scope.ytd-rich-grid-media {
display: none !important; }
/* The size of the text in the thumbnail title > in the channel name > number of views and upload date */
a#video-title.yt-simple-endpoint.style-scope.ytd-grid-video-renderer,
#video-title.style-scope.ytd-rich-grid-media {
font-size: 1.3rem; }
ytd-channel-name#channel-name.style-scope.ytd-video-meta-block {
font-size: 1.2rem; }
div#metadata-line.style-scope.ytd-grid-video-renderer,
div#metadata.style-scope.ytd-video-meta-block div#metadata-line.style-scope.ytd-video-meta-block {
font-size: 1.1rem; }