Hello MW,
Welcome to the Microsoft Q&A and thank you for posting your questions here.
I understand that you can't access US Unified Tax Prebuilt Model in Document Intelligence.
Definitely from the link you shared, we can see that the model currently supports specific tax forms such as W2, 1098, 1040, and 1099, which your file is supported.
However, make sure that the documents you are uploading meet the input requirements specified for the model. The model supports various formats like phone-captured images, scanned documents, and digital PDFs and refer to the latest documentation to ensure you are following the correct steps. The documentation provides detailed information on supported tax forms and how to use the model in the link: https://learn.microsoft.com/en-us/azure/ai-services/document-intelligence/prebuilt/tax-document?view=doc-intel-4.0.0
I hope this is helpful! Do not hesitate to let me know if you have any other questions.
Please don't forget to close up the thread here by upvoting and accept it as an answer if it is helpful.