Obsolete computer?

No, you don't need a new computer. You just need to use a new browser other than Safari. Since Safari was deemed part of macOS it only gets updated when macOS does. Your Safari is long out of date for current websites.

There are a good number of excellent replacements for Safari. Firefox (Mozilla), Chrome (Google), Edge (Microsoft), Brave, Opera, and so on.

I personally recommend Firefox.

It honestly depends.

If you find that your 2012 MacBook Pro is becoming quite slow or isn't able to keep up with daily tasks, look into upgrading to a newer Mac

You also stated that you are currently running macOS High Sierra and your Mac is a late 2012 13-inch model. Those models can run macOS Catalina and that is the most recent version of macOS they can run. If you aren't looking into upgrading your Mac, you might want to try updating your Mac to the latest version.

Try a different browser. I think FireFox has a version that will work on that computer.

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