With the later versions of iOS supporting "Files" now, Strongbox points to the file that is stored within the "Sync" (Resilio) location. What this means is that Strongbox is actively reading/writing to that file within the "Sync" location on iOS. Whenever I open the Resilio Sync app it will either push the changes I made on mobile to the server or pull down the file from the server and overwrite the file on iOS, depending on which is the newer file.

Also, I don't use Resilio's proxy servers either, so all of this is 100% running on my own infra. I have Wireguard setup on my home network, so if I am away from home, I can "VPN" in on my phone and then open the Resilio Sync app to sync up remotely.