“A lethal dose of cyanide is around 50–300 milligrams (mg). A 2018 analysis of previous research states that a person would have to eat around 83–500 seeds to develop acute cyanide poisoning.” Medical News Today, citing 2018 Oxford analysis

A redditor also did the math on how many apples that would be: "Apple seeds can release as much as 0.6 mg of Cyanide per gram of seed.

The average apple seed has a mass of 0.756 grams

The average apple contains 8 seeds

Therefore there are approximately 5.25 grams of apple seeds per apple, yielding a theoretical maximum release of 3.25 mg of cyanide from one apple

The lethal dose of Cyanide is based on body mass and is listed as 1.5 mg/kg.

A human can ingest about 41% of the lethal dose before seeing any side effects.

41% of 1.5 mg/kg = 0.615 mg/kg

The average adult male weighs 81.6466 kg (180 lbs)

Therefore the lethal dose in the average male is 50.213 mg.

50.213/3.15 = ~16 Apples

Therefore the average male can consume ~16 apples without feeling any side effects."