Maximum number of variant SKUs
100. If you get an error message while attempting to add variants to a product, it means that you've exceeded the limit of 100 variants per product. This limit cannot be raised for any account or plan.
Maximum number of pivot attributes (aka options)
You can only have a maximum of 3 options per product, for example Size, Color and Style. Note that these options can differ from product to product. This limit of 3 cannot be raised for any Shopify account or plan.
Resource: Variant Limits (Shopify Help Center)