Can the Polish employees stop complaining on Slido about not being successful for promotion opportunities?
Just because you were rejected doesn't mean there is some conspiracy. If you actually opened your eyes you would see plenty of promos and roles have been filled in Poland. Its one of the largest CSC hubs.
In my experience, my Polish counterparts lack a willingness to expand their remit outside the polish market let alone globally.
Take some time to work on yourselves and develop your corporate skills. Get comfortable with working across the region and with new cultures and your career will grow.