Using QB Desktop Enterprise 2021. 

With 5+ hours of trial and error I was able to import excel FY budget for Oct 2021 - Sept 2022 successfully. 

-In the IIF file enter the Startdate as 10/1/2021 for the portion of the FY for Oct 2021 - Dec 2021 and left the remaining 9 months of cells blank. 

-For Jan 2022 - Sept 2022 I entered the Startdate as 1/1/2022 and only entered 9 months of the budget and left the remainding 3 months blank. I even used the class.  

I was able to import it by prompting QB to ignore errors.