However, in practice, a remote worker can move anywhere, create a company (in the country where they live), send invoices and get paid. The catch is you need to take care of more taxes and admin work and there are none of the employee protections. You're essentially providing B2B services.
So, there are no legal issues for your old employer, as long as you're comfortable with that. It's mostly that employers would rather own you, as that gives them certain rights and benefits vs. just purchasing services from a contracting firm.