You may have seen advice from Lawyer's in the USA talking about the legality or effective protection by registering your work with third party websites such as Nuaivo.
In the USA , citizens of that country have to register with the USA copyright office and in effect bypass the Berne convention . However, and here is the IMPORTANT detail.
The U.S. officially signed onto the treaty through the Berne Convention Implementation Act of 1988, and it went into full effect in the country on March 1, 1989.
How it functions under U.S. copyright law involves specific guidelines:

Automatic Protection for Foreign Authors Because the U.S. is a member state, any creative work originating from another Berne member country (such as Spain, Mexico, or the UK) receives automatic copyright protection in the U.S. the exact moment it is created. Foreign authors do not need to register their work with the U.S. Copyright Office to hold a valid copyright or to file a copyright infringement lawsuit in a U.S.
That being said, this protects your work but your claim for monetary compensation has advantages when regestering your work.

Statutory Damages and Legal Fees Though foreign creators can sue without registering, the U.S. Copyright Alliance highlights a massive incentive to register anyway. To collect statutory damages (monetary compensation set by law without needing to prove actual financial loss) or to have legal fees paid by the losing party, both domestic and foreign creators must register their work with the U.S. Copyright Office.

Filing CostsSingle Application
($45): For one work, created and solely owned by one individual author who is also the claimant, and not made for hire.
Standard Application
($65): For a single song that does not qualify for the Single Application, such as a co-written song.
Group of Unpublished Works ($85): For up to 10 unpublished works created by the same author.

To summarise :- Under the Berne Convention creators/artists from outside the USA are covered by copyright and able to sue . If the creator wants to collect statutory damages (monetary compensation set by law without needing to prove actual financial loss) you need to register with the U.S. Copyright Office.
Advice would be to register your work with NUAIVO.com. at minimal cost. If your work show promising results enough to warrant the next step, then make the decision to register with U.S. Copyright Office. Until such time , you are safe in the knowledge that you are covered by the Berne Convention.

The Berne Convention has 182 member states (contracting parties). Because listing all 182 countries would be overwhelmingly long, they are organized below by major global regions.

Europe & North AmericaVirtually every country in Europe and North America is a member, including:
North America: United States, Canada, Mexico
Western & Central Europe: United Kingdom, France, Germany, Spain, Italy, Belgium, Netherlands, Switzerland, Austria, Ireland
Nordic Countries: Denmark, Finland, Norway, Sweden, Iceland
Eastern Europe: Poland, Romania, Ukraine, Russian Federation, Czech Republic, Hungary, Bulgaria

Latin America & the CaribbeanThe treaty covers nearly the entire region, protecting creators across:South America: Argentina, Brazil, Chile, Colombia, Peru, Venezuela, Ecuador, Bolivia, Uruguay, Paraguay
Central America: Costa Rica, Panama, Guatemala, El Salvador, Honduras, Nicaragua
The Caribbean: Cuba, Dominican Republic, Jamaica, Bahamas, Barbados, Trinidad and Tobago
Asia & the Pacific Major economic hubs and nations across Asia and Oceania are signatories
:East & South Asia: China, Japan, India, South Korea, North Korea, Bangladesh, Pakistan, Sri Lanka
Southeast Asia: Indonesia, Vietnam, Thailand, Philippines, Malaysia, Singapore, Brunei, Cambodia
Oceania: Australia, New Zealand, Fiji, Tonga, Vanuatu, Solomon Islands
Africa & the Middle EastA vast majority of African and Middle Eastern nations are integrated into the convention:
Africa: South Africa, Nigeria, Egypt, Kenya, Morocco, Algeria, Ghana, Ethiopia, Côte d'Ivoire, Senegal, Tanzania, Zimbabwe
Middle East: Saudi Arabia, United Arab Emirates, Israel, Turkey, Jordan, Qatar, Oman, Kuwait, Lebanon