I use X-plore File Manager in the tv box and in mi cell phone, it has a wifi sharing file service that gives you an ip address with te port, so you can use an web browser to upload files to it, it works fine, I just upload a video from my wedding to an USB attached to my tv box (Xiaomy My box S) from my laptop without any problems, even my son was watchin other thing in Disney + without lag meanwhile the file was uploading. You can keep it allways on, read only, password protected and other features, I have payed the app, but its whort it.
My get up is Banana Studios SSH server on the tv and mixplorer on my phone. I went into the router and gave the tv a static ip. This lets me resume files if their is an error.