Upgrade Martis Theme from Drupal 8 to 9

Hi Support,
How do I upgrade a Drupal Site with the Martin Theme from 8.9.10 to the latest version 9.
I tried everything and the site keeps on breaking



First of all, make sure the theme is compatible with the D9.
Secondly, it’s not an upgrade, it’s actually a migration ( from d8 to d9 )

Thank you very much for your reply.

I downloaded the D9 Version of the theme and side by side copied the D8 site into it.
Cumbersome, but it worked OK.

Best regards,