Can’t update theme

I’ve inherited a website once created using the enfold theme version 4.5.7. It seems not to be working with PHP 8.0. So I have to update to a newer enfold version. Since the developer is gone and nobody knows about the license, I purchased a new one, created a token and entered it in the update section. The key was accepted, but no update via wordpress took place. The update via FTP doesn’t work, because on the how-to-page is stated that a child-theme is required. Sadly, the developer didn’t build a child-theme. So I tried the export function of the old theme and imported the export file to the new theme. That worked for the most part, but the font type does not look so good. So my question is: Is there a possibility to do an FTP update without a child theme? If not, what causes the font problem? I haven’t found any settings with regard to the font type in the enfold theme.