FreeTube is supported by the Privacy Redirect extension, which will allow you to open YouTube links into FreeTube. You must enable the option within the advanced settings for it to work.
In order for the extension to work properly, you must be using an installable, non-portable version of FreeTube. This is because non-portable builds do not setup the required protocol needed for your operating system to redirect the URLs over to FreeTube.
The following builds are supported:
If you have issues with the extension working with FreeTube and you are using one of the supported builds, please create an issue in the FreeTube Repository instead of the one for Privacy Redirect. Most if not all problems is a problem with FreeTube itself and not a problem with the extension.