My website is indexed and ranking well. I can see the posts with the videos in the "All" tab.
Sadly not a single one of my posts is visible in the "Videos" tab and 99% of the content is videos.
I’m using a video sitemap.
I see you have tagged this post with video sitemap so I am assuming you have one functioning on your website? Have you also submitted this to Google Search Console? I would also recommend using schema mark up to aid your appearance in video results. This Google Developer article covers video sitemaps and schema mark up in an overview and links out to the more in-depth details of the best practice for both.