When asked how much income my dependent had do I type in how much social security disability my dependent received in 2021? Also true for SSI benefits?

No.  SS and SSDI  are not taxable income so is not included.

Did your dependent have any other type of income in 2021?  If so, some of the SSDI (but not SSI) might be taxable.

More generally, though, who/what is asking you how much income your dependent had?  Is this for, say, a student loan or something other than income tax?