Hey @Slemming
Even though this feature is not currently available in Shopify out of the box, I can recommend checking out the Arigato Automation app that can help with this. With this app, you can automatically add products to collections based on a metafield value.
To quickly get started on this, you can download the following sample workflow from our automation library: Add Product To Collection Based On Metafield in Shopify by Using Arigato Automation.
Feel free to contact our team if you need a hand with the configuration. 