The PPP grant is not federally taxable. I am unaware of any states that tax it. Oregon doesn't, which leads me to think no state does, because Oregon will tax anything they can. They would tax air if they could.
However, there are other COVID-related grants that ARE taxable, so make sure you confirm that your client's money is actually PPP and not some other grant.
PPP was not a grant. It is a loan, which can be forgiven if you apply for forgiveness and meet the requirements.
Receipt of a loan is never taxable income.
The loan forgiveness is not taxable for federal. Each state has its own rules for their treatment of the loan forgiveness or deductibility of expenses paid with PPP loan money.