Video pages not being indexed

Hey guys, We have a "videos" section in a guides blog, under a commercial website. At first, we had the videos embedded through Youtube non-listed (over 18). In addition to the video, we have a paragraph describing the video. These pages were not indexed, despite having them on sitemaps, internal links and submissions through GSC.

We noticed that GSC doesn't show the video preview (Gray background). We switched the videos to be embedded with Vimeo. GSC shows a preview, but only one video is indexed out of more than 20.

GSC shows "No: 'noindex' detected in 'robots' meta tag", but everything is open to index.

What could be the issue?