Posted a while ago on HN:
https://slimemoldtimemold.com/2023/07/24/your-mystery-have-a...
A good litterature survey, easy to follow. Better than reading one or two isolated studies, since it does ask the crucial question of "well what is (and how do you measure) attention span anyway?"
Less rigorous but similar conclusion in video if you prefer https://youtu.be/aDfeOvUZ7Kk?feature=shared