If rolled out widely, this would make web browsers and third-party YouTube clients without a DRM license unusable for YouTube playback, download, etc. This would include almost all open-source web browsers and almost all third-party YouTube clients. Archive link to reddit post about this
SmartTube?
I just let it roll through the 403 “Applying the fix”.error while I did something else. Took maybe 5–10 mins, but started playing and no issue since.