If you don’t want to create a new default category, you could just rename ‘uncategorized’ for your website.
To do this, all you need to do is to go to the dashboard, ‘posts’ and then the ‘categories’ page. Then you need to find the ‘uncategorized’ option and then click on the ‘Edit’ option. This allows you to change the name and slug of the category for your website.
Remember that if you’re changing the slug of the category, then you can have 404 errors that can appear on your website. You might need to add a 301 redirect to your website to ensure that any existing links are redirected to your website.