Hello Sandra,
Thank you for reaching out.
> The tag restriction will work only after the user bought 1 of the product
Can you please elaborate on this? Are you saying the tag restriction should only work when a user purchases a product, or do you want to block guests from purchasing products beyond the limits?
If you want to block guests from purchasing products beyond the limits, then please navigate to WooCommerce > Settings > Maximum Products per User > General and set Guests to Do nothing but block guests from purchasing products beyond the limits option.
Please let me know if you need any help.