A home generator such as a Generac that is professionally installed is not a medical expense. It's a property improvement that adds to the cost basis of the property. This does not get reported anywhere on your tax return and will not come into play until the tax year you sell the property.
If this is a portable generator, it's a personal expense and not deductible anywhere at all.
The problem is that home improvements are not tax deductible medical expenses even if the improvement is necessary for medical reasons. Unless the improvement costs more because of the medical need, or the improvement does not actually raise the value of the home.
For example, the IRS recognizes that installing grab bars to make bathrooms and showers safer, while technically a home improvement, usually does not actually raise the value of the home, and so the cost may be deducted as a medical expense if it is medically necessary.
Likewise, the full cost of a wheelchair accessible van is not a medical deduction, but the extra cost of the accessible conversion may be a deductible medical expense.
A generator by itself is not a deductible medical expense, but if you have to purchase some extra equipment or upgrade to make it more suitable for the medical requirements, that extra cost might be a deductible medical expense. If audited, you would need documentation from your physician about the medical need and you would need documentation from the installer or the manufacturer describing how the extra cost is related to the medical need.