Hey @GuidoD - indeed there is!
If you go to System Console > Customization > Posts, there is a setting for enabling/disabling website link previews. If you turn that setting off, it’ll disable all link previews, including YouTube previews.
https://docs.mattermost.com/administration/config-settings.html#enable-link-previews
Note: Make sure you have Mattermost 5.4 or later installed. Earlier versions had a bug where YouTube previews were not affected by this setting.
Let me know if you have any questions 