If you need Astro, you do not need a component library
Astro is designed to minimize the amount of JavaScript required to build a website. All component libraries require quite a bit of JavaScript to work, so if you are planning to use Astro, the best option is to build your own components that do not have large footprint.
I need Mantine, what should I use instead?
In case you need Mantine and SSG application, you can use Next.js or Gatsby. Both of them support all React features that are required for Mantine to work.
No! I need Astro and Mantine!
Not a chance, according to Astro documentation, Astro does not support React context, which is required for Mantine to work.
From Astro documentation:
UI frameworks like React or Vue may encourage “context” providers for other components to consume. But when partially hydrating components within Astro or Markdown, you can’t use these context wrappers.