This is answered at poster's other post https://ttlc.intuit.com/community/state-taxes/discussion/turbo-tax-state-return-for-ohio-is-in-error...
TT is doing it correctly. There is nothing to fix.
Ohio's method of tax calculation, for non-resident's is convoluted, and hard to understand and/or explain. Ohio first calculates what the tax on all your income would be, applying all deductions and credits, including the Joint Filing Credit (JFC). So, the JFC is only used to reduce the tax calculated on all the income ("Ohio Adjusted Gross Income", which includes the NY income). Then it applies the separate non-resident credit, to effectively tax only the OH income.
