Setting output for Related Products to In Stock only

I’d like to figure out a way to ensure Out of Stock and On Backorder products are not offered as Related Products. I realise this is a much-asked questions with a wide variety of snippets offered as solutions, but I’ve not managed to find one that works correctly (possibly the ones I’ve found, including the many threads here, are out of date).

Do clarify, I do want Out of Stock and On Backorder products to be visible in the shop and search, just specifically not in Related Products.

Any advice would be much appreciated. Thanks!

The page I need help with: [log in to see the link]