Whenever you have questions regarding taxes, it is best to consult with an expert, such as a lawyer, it is the safest thing.
However, a non-formal summary.
Itch is a store in the USA, in the USA if you sell something, your profits must be reported to the IRS using a number that identifies the person or company that is earning those profits. The numbers used are the following:
Social Security number "SSN"
Employer Identification Number "EIN"
Individual Taxpayer Identification Number "ITIN"
Taxpayer Identification Number for Pending U.S. Adoptions "ATIN"
Prepare Taxpayer Identification Number "PTIN"
IF you are a citizen of the USA, you will have an SSN, if you are a company from another country that is going to generate profits in the USA, you can request an EIN or an ITIN from the IRS. But this is a legal procedure and it is best that you consult with a specialist.
Itch, unlike Steam, allows you to sell your content without having to have one of these numbers.
If you apply for an ITIN, you can access agreements, for example, to get your tax money back, however it is not simple or cheap if you are just a natural person who wants to casually sell their games.