Yes, you can deduct at least part of the cost of installing a handicap ramp if your mother is your dependent.

 Per the IRS, the cost of the improvement is reduced by the increase, if any, in your property value resulting from the improvement you made.

The IRS also states that "Certain improvements made to accommodate a home to your disabled condition or that of your spouse or your dependents who live with you, don't usually increase the value of the home and the cost can be included in full as medical expenses."

This information can be found by clicking here.  Start reading at the Capital Expenses section.  The handicap ramp is the same as "entry or exit ramps" mentioned in the IRS Publication.

where do you enter a medical expense for installing  a handicap ramp...i know its deductible but cannot find where to enter

You are correct - it is deductible Just enter it as an "Other Medical Expense", the last screen in the Medical Expenses interview (see sample screenshot, below).

From  Publication 502 (2020), Medical and Dental Expenses:

Certain improvements made to accommodate a home to your disabled condition, or that of your spouse or your dependents who live with you, don't usually increase the value of the home and the cost can be included in full as medical expenses. These improvements include, but aren't limited to, the following items.

• Constructing entrance or exit ramps for your home.