"is an irrevocable trust (due to death of settlor) a simple or grantor trust?"
Most trusts written with the settlor as trustee and beneficiary while the settlor is alive are revocable and/or have other features that cause the trusts to be grantor trusts while the settlor is alive.
Upon the settlor's death, such trusts generally become irrevocable and are no longer grantor trusts. You need to refer to the trust instrument, itself, but the trust is now most likely either a simple trust or a complex trust.
See https://www.irs.gov/instructions/i1041#idm140376226642960
"is an irrevocable trust (due to death of settlor) a simple or grantor trust?"
Most trusts written with the settlor as trustee and beneficiary while the settlor is alive are revocable and/or have other features that cause the trusts to be grantor trusts while the settlor is alive.
Upon the settlor's death, such trusts generally become irrevocable and are no longer grantor trusts. You need to refer to the trust instrument, itself, but the trust is now most likely either a simple trust or a complex trust.
See https://www.irs.gov/instructions/i1041#idm140376226642960