Sort WordPress Archive by multiple oderby arguments in pre_get_posts action

I am not an expert, but you have a couple of issues here

Firstly, is_archive() should be an object of $query. You should also just target the front end with your function. Remember, pre_get_posts alters all instances of WP_Query, front end and backend.

So this line

if(is_archive() && $query->is_main_query()) :

should look something like this

if( !is_admin() && $query->is_archive() && $query->is_main_query()) :

I can’t figure out your logic with your meta_query and your ordering. I’m really not to sure if your ordering will really work. You should have a real look at that as you are specifying one key and sorting by another

One other possible issue I can see here is, you are using the OR relation in your meta_query. You are retrieving post which have one meta_key or the other meta_key. What happens when there are no posts having one or the other meta_key. How will this influence your ordering and what errors if any will be triggered. Frankly I have not tested scenarions like this yet, so this might be a grab at nothing, but still useful to keep in mind

You might need to work in some check to make sure that a key exists before you try to orderby by it.

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