My FreeTube stopped working today, so I figured others would also be affected.

The devs posted a temporary workaround on GitHub:

• Set Primary API to Invidious in the General Settings

• Select an Instance that is near to you, see https://api.invidious.io/. Make sure to pick one that has a checkmark in the API field. Also make sure you start typing the instance name with https:// and it should list instances as suggestions.

• Disable Fallback to Non-Preferred Backend on Failure in the General Settings

• Disbale Proxy Videos Through Invidious in the Player settings

This seems to be working for now, until the (awesome) devs release an update to fix the issue.