Shopify limits product.variants in Liquid to a maximum of 250 items. Even if your product has more variants (e.g. 500), Liquid will only give us access to the first 250. This affects any Liquid-based output, including JSON-LD structured data.
As a result, when generating JSON-LD using Liquid, we can only include the first 250 variants in the offers array. The rest are simply not accessible.
There’s no way to access more than 250 variants in Liquid directly at the moment. This is a platform limitation.