Safe, easy to install, highly customizable. Cons: Does not actually change the underlying site code, just the visual presentation.
: You can change the logo to older versions, restore the small video player, and bring back the classic grid layout with smaller thumbnails. CustomTube
: This extension allows you to cycle through layouts from 2008 to 2021. How to use
If all else fails, change your mindset. Use RSS feeds to pull new videos from your subscriptions into a reader (like Feedly). That bypasses YouTube’s UI entirely, giving you the spirit of old YouTube without the actual app.
Note: YouTube’s interface and features change over time; older versions may no longer be supported, can lack security fixes, and might violate terms of service. Proceed carefully and at your own risk.