See the "insert link" button?
Use that for any URLs that
aren't images
nor YouTube videos.
To its' right is the "insert image" button,use that for image URLs(you can't upload images).
For Tenor GIFs specifically,open the Tenor GIFs' page,right click n' open into a new tab,then head to that tab to right click n' open into a new tab,that second new tab contains the direct URL for the Tenor GIF,ensuring it embeds properly.
Two more steps to the right is the "Media" button,use that bad boy for YouTube URLs(others are very much hit or miss),but make sure you use a full YouTube URL,"
https://www.youtube.com/watch?v=",not the short form ones that mobile uses,along with getting rid of the "&pp=" or "&si=",if you want to embed a YouTube Short video,replace the "
https://www.youtube.com/shorts/" with "
https://www.youtube.com/watch?v=" to turn it into a normal video.
That should get your memes through better.