Commercial themes from theme marketplaces like Theme Forest can be purchased for a one time purchase.
However, the license to receive further theme updates must be renewed every 12 months.
So, to keep your website secure and safe, Theme Forest theme licenses should be renewed every 12 months.
To purchase a commercial theme for a one time purchase which includes all further updates, what you’re looking for is a lifetime license.
Excellent website builders like Elegant Theme’s Divi has a lifetime license available. A yearly license is $89, while a lifetime license is $249.