My fiance is disabled and lived with me in 2020. I didn't track expenses. Is there a standard deduction for other dependent?

No.   All you "get" for claiming a qualifying relative---which is the kind of dependent your fiance would be if he can be claimed -- is a $500 credit for other dependents which can lower your tax bill.   You do not get stimlus money for claiming your BF/GF   --- and he does not get stimulus money himself because dependents cannot receive the stimulus money.

CREDIT FOR OTHER DEPENDENTS

https://ttlc.intuit.com/questions/4499708-what-is-the-500-credit-for-other-dependents-family-tax-credit

My fiance is disabled and lived with me in 2020.

The fact they are disabled just doesn't play into this unfortunately. At best, they might qualify as a dependent under the "Qualifying Relative Dependent" rule, even though they have no relation to you.

https://apps.irs.gov/app/vita/content/globalmedia/table_2_dependency_exemption_relative_4012.pdf