The fact that you can't use this extension (amongst many others) with Safari - therefore Safari on MacOS and iOS/iPadOS cannot benefit from this type of sharing. Walled garden strikes again.
I'm not saying that Safari is a bad browser, but artificial limitations imposed by Apple on the browser and the OS is quite frustrating for me.
Safari supports the same extension standard as the other browsers, they even have a tool to convert extensions into the Safari format. All the bookmarks are also in an sqlite database which you can access, or export them as a file, this is not a case of a wallet garden.
I know because I did just that with my Firefox and Chrome extensions. The only thing that's keeping developers from doing that is that you have to pay the developer fee to publish the extension app, on top of the regular differences between the browsers that you have to take care of if you are building an extension.
That's all great but neither this nor www.xbrowsersync.org supports Safari.
That's the reason I don't use Safari beyond random superficial browsing.
Here is what xBrowserSync has to say about it:
"Will xBrowserSync support Safari?
No and it is extremely unlikely this will ever happen due to Apple moving away from the WebExtensions API and forcing developers to purchase Apple hardware and pay $99/year to develop on their platform."
