If you've decided to subtheme your site, it will be necessary to make certain that your info.yml file references the correct Core version(s) of Drupal (current and possible future) so modules and code will be compatible with your SiteFarm site.

Updating your info.yml file

Add the following line to your info.yml file: 

core_version_requirement: ^9 || ^10 

OR, if you wish to be proactive, you can include the notation for Drupal 11 so you'll be set for the next upgrade in the future, which would change the entry to read:  

core_version_requirement: ^9 || ^10 || ^11 

Remove this line if it exists in your info.yml file: 

core: 8.x 

After your file is updated, deploy your file to so it's live on your site.