kuaza sorry for the late reply, I've missed it.
kuaza Is there any way to achieve this?
Currently, there is no extension on Flarum (as far as I know) that allows you to link Flarum instances or setup an authentication/user provider (i.e. an OIDC provider that would pair well with my premium OIDC client extension)
kuaza Or how much do we have to pay if we want to print a plugin for it?
If someone wants to sponsor this feature you can write me via Telegram or live chat on my website to agree on the price and the availability date. Currently, I'm very busy with a lot of things and other projects, so I'm not sure this will be available very soon (even with a sponsor)