There are numerous fluxes available "for lead free solders".
Very few are suitable for stainless steel. Those will remove chromium oxide. It's a chemistry/metallurgy thing!
Easyflo flux doesn't work particularly well unless the chromium content of the steel is low. That is why silver solder suppliers have a bespoke flux. Again it's a chemistry metallurgy thing.
Good luck with getting hold of easyflo silver solder. Its sale was banned years ago. HSE and Trading Standards still have a more than passing interest in its availability. I, like a lot of people, still have some but it's not for sale.
Using it is not illegal. Selling or giving it away is.
If you want more information, then get my book!
Keith