YouTube on Safari causing high CPU and overheat, what should I do?

Temporarily, you can do something to decrease CPU % performance when loading in YouTube tab as following:

YouTube:

• Do not chose 2K or 4K video clip, indeed 1080 maximum resolution
• Disable playing when moving mouse option at: User -> Setting -> Playing and Performance

Safari:

• Clear cache & cookies at least 1 week
• Using Adblock premium

MacOS:

• Downgrade MacOS to Catalina, BigSur (in my opinion, Mojave is the best MacOS for all Intel Macbook)
• Enable Firewall and disable FileVault.
• At least 5.6GB free on your Macintosh partition.

Hope to help.

Thank you, @Todd0213.

If I want to eat a candy, I just put it into my mouth. And if the candies are in a box, I will open and eat them :D

(Please do not guide me something simply as delete cache, history, disable extensions ...)

No, I want to understand, why YouTube cause high CPU when using on Safari, just only YouTube tab but not also another.

Let take a keen on eyes to kernel_tasks, this is a complicated background processes, which might be created by something old language, such as C or even Assembly, an ancient one. The kernel_tasks works as more than one application, it will never breaks anything cause hang OS, at least as my understood.

I see, YouTube uses or prefer VP9 decode which just only comfortable to Chrome or x86_64, and it used software accelerator progression. Safari used hardware instead of, that's might be reason.