@Adam1234 if disabling and then enabling again like Evan123 mentioned, then I want you to check brave://components and see if you can update Widevine Content Decryption Module or if it comes back with an error.
If it comes back with an error:
It means you launched Brave as an administrator for some reason at one point and components got locked behind those admin permissions where it’s no longer able to be fetched by Brave. It may be someone using your device that did it or something “behind the scenes” within your OS that did it for some reason, though typically only occurs due to human interaction.
Anyway, the fix to it is basically what you see at Brave doesn't start when I run it as administrator and Brave Shield doesn't work - #41 by clifton which is to reassign the permissions again.
And if not clear on the description, try to never “Run as administrator” when opening Brave.