Following your limk it appears to me that only 46.6% [1], or 23132 deaths, of the unintentional poisoning deaths are classified as X42, or “Accidental poisoning by and exposure to narcotics and psychodysleptics [hallucinogens], not elsewhere classified” [2]. I can”t find any further split into fentanyl and non-fentanyl among those.

[1] https://wisqars.cdc.gov/data/lcd/drill-down?lcd=eyJjYXVzZXMi...

[2] https://icd.who.int/browse10/2015/en#!/X40-X49