I have this same problem, and I hope someone from TT support can suggest a solution. I've been able to use TT in past years to file IT-203-F for RSU income, but it no longer seems possible to do this. I have the downloaded version of Turbo Tax Home and Business 2021.
My situation is the same as @LavenderBeaver. I'm a NYS non-resident who receives part of my W2 income as RSU stock grants. Since these vest over multiple years, I need to use IT-203-F to allocate this income to NYS. I've tried this in both step-by-step mode and in forms mode, and the TT software seems broken in both cases.
In forms mode, I tried changing the "Allocate by Formula" drop-down to "M" (multi-year allocation) on the New York State Wages/Self-Employment Income Allocation worksheet, Part I (New York Wage Allocation). When I do this, TT does *not* add any IT-203-F form to my return, and it incorrectly excludes all of that income from NYS. If I manually open form IT-203-F, TT links the income to Schedule A (Current year allocation of income attributable to past employment in NYS). However, this is not correct in my situation. Instead, I want to allocate the income on Schedule B (Stock option, restricted stock, or stock appreciation right allocation). I've tried filling out Schedule B anyway, but TT does not link the result correctly back to the main IT-203 form.
In step-by-step mode, I see a similar problem. On the "Allocate Wages to New York" page, I tried selecting "Allocate over multiple years". This causes TT to create an IT-203-F form, but incorrectly links the income to Schedule A. Again, I can not find any way to fill out the information in Schedule B and get TT to link the result back to the main IT-203 form.
As @LavenderBeaver noted, previous versions of TT allowed you to manually fill out IT-203-F and attach a PDF to the return. It would be great if you could restore this functionality.
For others who have this same problem, the best solution I've found is to fill out the PDF version of IT-203-F (as you needed to do in prior years). Then in TT, select "Allocate by percentage". When TT asks for the percentage, enter the number you calculated on line 19 of form IT-203-F. This causes TT to allocate the income to NYS correctly. However, TT does not have any way to submit your IT-203-F with your return, so I fear this will invite an audit since the NYS Dept. of Taxation will have no way to know how you came up with that percentage.
