To set the default radio option for different products, you will need to access the Shopify theme editor. Here are the steps you can follow:
Navigate to Shopify Admin, go to Sales Channel --> Online Store --> Themes.
Click on 'Customize'.
Inside the visual theme editor, select 'Products' from the drop-down menu at the top.
Click on 'Default Product'.
In the 'Product Information' section, find the 'Subscription Plans by Ongoing Subscriptions' app block.
On the right-hand side, you can edit the 'Plan Selection Type' to 'Radio style' for subscription plan options or change the 'Purchase Type' to default to 'Subscribe & Save' instead of 'One Time Purchase' as needed.
Check Templates for Variations:
If different products use unique templates, repeat this process for each template to ensure consistent settings.