I mean, there is a secret way to filter for primary ship if that's what you're looking for?
You need to install a userscript in your browser, so if you're a mobile user you'll want to use Firefox instead of Chrome (Chrome doesn't allow users to install scripts in the mobile version of the app).
The script is called AO3 Only Show Primary Pairing and what it does is filter out fics that don't have your indicated ship as the first (or only) relationship tagged.
If you've never installed a userscript before, click or tap on the ? in green next to where it says Install this script. That'll take you through the process of doing it for the first time.
The code itself is commented, so you should be able to to just drop your info into it. They give you an example ship in the relationship field and you can add in characters as well (or instead) if you prefer.
You can also adjust how many tags it looks at. Default, it just looks at the first 1 but if you want it to look at the first 2 or 3, you can just adjust the numbers.
Edit: also I just realized this is a branch of this post that doesn't have my correction. To remove oneshots, the syntax is actually
-expected_number_of_chapters: 1