What does the so-called "immigrant country" mean? If I want to study in a European country and then work, can I live permanently?

This year, Britain abolished the policy of staying after graduation, which means that it is almost impossible for Europe to immigrate through studying abroad. As for Sweden and Norway, they are not immigrant countries, so they can't study abroad, apply for jobs after graduation, and then get permanent residency. In addition, permanent residency is the so-called immigration, and those who get permanent residency can enjoy all the welfare benefits of the country except politics. If you want to enjoy political rights and national passports, you must be naturalized. There are still many friends who think that they can apply for a work visa there first, and then they can immigrate after a few years. This idea is wrong. Before you have the status of this country, the possibility of job hunting is extremely low, and employers in any country will not be willing to hire an employee without the right of abode.