I personally use Ubooquity for this. I can use the OPDS functionality to read it on Koreader on my Kobo, and can use the web interface to read it everywhere else.
From the screenshots on their site it seems to be a web app, both the reader and the admin. So you must be able to reach the server every time you are reading an ebook. Did you install Ubooquity on a server on the internet (a VPS?), do you have a public IP address at home, do you use a tunnel from home to a server on the internet? And what if you don't have internet connectivity?
I host a local server for a bunch of services, including Ubooquity. I do most of my reading on my Kobo, through Koreader, and as I use OPDS to fetch the books for it, I also have them locally and do not require internet access.
Not having internet connectivity is never a problem for me, the entire region where I live is completely covered by 4G.
Does OPDS support sending to the server the current position in a book? That's basically the only feature I would need a server for. Books are synced with Syncthing, no need for anything fancier than that. Of course the ebook reader must be able to send the position to the server when in the same network.
I'm also almost always in 4G coverage but there are planes, trains, mountains, tents in the middle of nowhere, etc. Apps that work offline are a safer choice.
Open Publication Distribution System (OPDS) doesn't seem to include any tracking if how much you've read of a publication. So there doesn't seem like there would be any way to read across devices, which is something I too long for. https://drafts.opds.io/opds-2.0
