Hello! Did you get this issue resolved by now? I was having a similar problem but filed the same form on both itch.io and Steam in the same day; On the Steam side, I have to provide additional proof of identification (scans of government ID docs), but the process is already done by now. Here on itch I haven't got any feedback beside the pending status on my Tax Information page, and I believe both Valve and itch are using the same third-party company to process these kind of tax administration.
Viewing post in Tax Validation Inquiry
Hello!
So this is a yes and no.
They have validated my form but the withholding is still at 30%. Even though I have provided everything they need to see that Switzerland has a tax treaty with the US including the TIN (Tax Identification Number). Now I don't know if the 30% are accurate or not, but I have not gotten a reply from the Itch support nor the tax support on that matter or about my questions either.
So it only is partially resolved