Hi @mikeyl567
the instructions you read around are indeed correct.
Please follow this guide. I’ve just tested on Minimal Theme and it works and it should work on all themes, if they are implemented following Shopify guidelines.
Go to your backend in Settings > Metafields and click Products
Click Add Definition to add a new product metafield.
Name: Metafield name (e.g. Hide Product)
Namespace and key: seo.hidden
Description: up to you
Type: Number [Integer]
At this point, if you Edit any product you’ll find a new metafield at the bottom of the page: just fill it with 1
I hope it helps