Hello,
Those are immature acorns. They look like the come from a tree in the red oak family? That would include red oak, black oak, and a few other species. The red oak side has pointy leaves with bristles on the tip while trees in the white oak family have rounded leaves. The article below explains the difference using pictures. 
https://www.canr.msu.edu/resources/smart-gardening-identifying-the-oaks-of-michigan
Oaks in the red oak family develop acorns over a period of two years. So, the flowers that were fertilized in May/June of 2023 are the origin of the mature acorns that will drop this fall. 
These look like they may have been chewed off by a squirrel? It's common for oaks (and other trees) to drop immature fruit/nuts. So, nothing to worry about. 
Trees often produce a mass amount of fruit or nuts in what we call "mast years." The article at the link below explains what a "mast year" is:
https://www.massaudubon.org/news/latest/about-those-acorns
The article lists that a mast year occurs every 2-5 years; I've seen longer spans of time between mast years. That, coupled with a frost/freeze that regularly occurs at the end of May, when oaks are flowering, that effectively kills the flowers result in a longer time frame between mast years. 
So, a variety of factors at play! For now, I hope you enjoy the shade of your giant oak tree. 
If you have any questions, please feel free to reach out. 

Thank you,
-Julie