There are many studies.[1]

Large-scale genetic studies have found markers associated with self-reported "morningness".[2][3] At least some of these markers are near genes known to affect circadian rhythms.

Observational studies control factors like caffeine intake and light exposure.

[1] https://en.wikipedia.org/wiki/Chronotype

[2] https://www.nature.com/articles/ncomms10448

[3] https://journals.plos.org/plosgenetics/article?id=10.1371/jo...