You want to link all products from an existing catalog to a new view/website within your magento 2 multistore
You can do this using the following query. Just be sure to backup in advance
Make sure you know the website_id of your new view before proceeding
INSERT IGNORE INTO catalog_product_website
SELECT entity_id, {website_id} FROM catalog_product_entity
Replace website_id with the id of your new view, for example, if it is 3, you will get::
INSERT IGNORE INTO catalog_product_website
SELECT entity_id, 3 FROM catalog_product_entity
Then reindex everything
Normally: php bin/magento indexer:reindex
With memory limit: php -dmemory_limit=512M bin/magento indexer:reindex