Only the windows executable version can load mods from files for security reasons. Every other version is just the browser version, and browsers have various security features that prevent file system access and “fuzz” local file paths, so this is a hard limitation.
In order to load a mod in the web version, it needs to be hosted on the web or localhost, and the URL entered into the game. This is the only way. I host all first party and several third party mods on my personal website for use in the web version.
I do not host romance unlocker, and don’t plan to. For one, I have no way to contact the author, and I cannot host someone’s file without their permission. On top of that, it’s actually buggy and messes up the dates and other romance features.