'imgbb' (or 'ibb' as it appears on the links generated by the site) stands for 'image bulletin board' because it can
onlyhandle images.
As Mp4 is video format, the obvious way to share your files with others is to upload them to YouTube. However if you, say, want to send an Mp4 video file to a friend (rather than having it viewable on a website) you can use one of the many free file transfer services:
https://www.techradar.com/uk/best/best-ways-to-transfer-files-online
My own preference for transferring (any type of) files is dl.free.fr. It's (almost) all in French but it's actually very easy to use:
http://dl.free.fr/
Click 'Choose file'.
Navigate to the location of your chosen file and double-click on it.
Click 'Envoyer'
You'll then see a bar showing the upload progress of your file, followed by a message (in French) telling you that the file is being processed.
When you get to a box with the words "Le fichier sera accessible à l'adresse suivante", right-click on the link to the right of it and copy it. That's the link that you need to send to your friend or, say, to post here if you want to share a file with us.
You then simply need to tell the recipient of the file to go to that we address and click on the grey box to start the download process to their computer. (That's the method I use to share crossword files with other AB members).