Elias here with Shopify Support. That’s a great question!
I understand you’re looking to add a meta title and description for the ‘All Collections’ page. It's possible to add the meta title and description through the theme’s coding, by adding it to theme.liquid. This theme file is dynamic and can apply to specific pages.
It's important to note that this requires advanced knowledge of coding as it involves custom coding. Using the Brooklyn theme as an example, the 'All Collections' page outputs the page_title object as 'Collections' and can help theme.liquid apply the meta title and description to that page. Then, you can add the meta description using the page_description object. That being said, if you’re using a third-party theme, I recommend double-checking with the theme developer on where you can add the meta tags for 'All Collection'.
Here's where the meta title and description is located in the Brooklyn theme:
I'm glad to hear that you're comfortable with coding, as this does fall outside our design policy. However, if you run into any roadblocks, I recommend having a developer or expert to help you with this. If you don't have a developer, feel free to find a developer on Shopify Experts. Shopify Experts are experienced with custom coding and they will be able to help you create a solution for this.
I hope this helps. Let me know if you have any further questions.