If you are a contractor without a business, and just receive the compensation to your personal account, then I think from UAE's perspective you just count as a natural person making money, and in this case there are no registering requirements and no tax︀ for turnover below 1M AED.
If you instead a are contractor with a foreign business,︁ then you probably have effective management and control / PE in the UAE, and then︂ you have to register, and do tax filing (as per current rules at least, Im︃ kind expecting a gap between rules and application/enforcement for foreign companies).
And in both of︄ the above cases you can get a remote worker visa and you dont need a︅ sponsor. Or you can get a property visa - no sponsor needed there either.