If you go to https://shopify.dev/docs/themes/liquid/reference/objects/block#block-type there is a link where it says: Returns the type defined in the block's schema.
That link takes you to https://shopify.dev/tutorials/develop-theme-use-theme-editor#blocks which doesn't seem to have any content regarding that. There is a mention to "Content Types" on the menu on the right, but clicking on it doesn't show anything. The last item with actual information is Merchant Settings.
So where can we find documentation on the block types available?