I took a look at our upcoming 2021-07 Release Notes and our Developer Changelog, where larger API changes and releases are usually documented, and couldn't find reference to any changes around Refund or RefundLineItem.
To get a better idea of which upcoming changes you are referencing in your post - would you be able to share a screenshot or link to the resource you are following? With this, I'd be happy to take a closer look or pass on any insights I can!
My app listens to the "orders/created" and "orders/updated" webhook events, and goes through the line items and reports sales to another platform with the purpose of maintaining inventory counts across both Shopify and our service. This includes reporting refunded items that are restocked, since they'll be available again. If there is no change to the Refunds or RefundLineItems arrays in the JSON events that are sent to those webhooks then there will be nothing to change in advance of the July 1st changes.