This might be a bit much, depending on your experience with docker and bash, but I uae this framework/platform to selfhost many apps and services, and qbittorrent via wireguard (using mullvad) is one of them: d.rymcg.tech
That link is to the main page of the project, which explains how to set up and use the framework/platform. From that page, you can get to the qbit torrent-wireguard app, or here is a direct link: d.rymcg.tech/qbittorrent-wireguard.
Once you get used to the platform, it’s quite easy to use, very customizable and versatile, and follows good philosophy of seperating your data from the app. And while it may be more advanced than you’re looking for, it’s very well documented, making it pretty easy to just follow the required steps.