I would like to add that I have encountered this problem as well. If you visit the Odoo sample database and attempt to click on the "Recurring" option for any storable product, there is no error. 

If I visit my older upgraded database (Odoo 16 which has been active since Odoo 14) I get the error  A 'Storable Product' cannot be a 'Subscription Product' !

Somehow the older database did not allow this, but the newer one does? I have no clue how to fix.

Steve.

None of that targets what I'm talking about.

The issue isn't how to do recurring storable products, the issue is that when clicking on "Recurring" when storable product is selected, a warning message appears and unchecks "Recurring".

Hi,

To create a new subscription product, navigate to Subscriptions app ‣ Products ‣ Products, and click New.
The Recurring option is enabled by default, prompting Odoo to recognize it as a subscription product. Be sure to leave the Recurring and Can be Sold options enabled.
The Product Type field is set to Service.

For more details, refer to the blog:
https://www.cybrosys.com/blog/how-to-create-a-new-subscription-product-in-odoo-16-subscription

Hope it helps