A cleaner Google Shopping feed
Activate the product feed, sync shipping, then include each product. Sibling feeds sit next to this screen.

A cleaner feed is fewer rejected items in Merchant Center.
Open Marketing and sales → Google Shopping. Set Product feed to Activated. Sync shipping if you want rates in the feed.
On each product, turn on Google Shopping feed sync so that item is included.
Facebook catalog and TikTok feeds sit as sibling screens next to this one. They are not this page.
Questions about the Google Shopping feed
Marketing and sales → Google Shopping.
Product feed must be Activated, and the product needs Google Shopping feed sync on.
Facebook catalog and TikTok feeds are sibling screens. They are not inside Google Shopping.
Send a cleaner feed to Google
The settings are already in admin, under Marketing and sales.