How to create a Pages template using Shopify API

[rg18]

My Shopify App has a feature that creates a Page using the Pages REST API, for my merchants. In these pages, merchants can add my apps' app blocks. Right before the pages endpoint creation is called, we use Asset API to create a template file. This template file is sent as the `template_suffix` parameter when creating the new Shopify Page.

Now that PUT and DELETE requests to the Asset API are being deprecated, what is the alternative for creating a custom template file to use during the creation of the Page? Is it something achievable with theme app extensions?

Thank you very much!