Normally, we could create site designs and register them in SharePoint to one of the modern template sites: a group-connected Team site(WebTemplate ID is 64) or the Communication site(WebTemplate ID is 68).
If you have disabled modern Group creation, you could publish your site designs using WebTemplate 1 so that they display for the "Group-less" Team site template.
So the newly registered site design will not be displayed under inconsistent web template when you create a new site, however you can apply the site design to current site via site settings> Site Designs which will show as expected.