Here's a little information on O blood:

Although the blood type O+ can donate blood to all positive blood types (A+, B+, AB+, and O+), it is not a universal donor. Blood type O- is the universal blood donor, meaning that people with this blood type can donate blood to all other types with a lower risk of causing serious reactions.

https://www.medicinenet.com/is_o_a_universal_donor/article.htm

O negative blood is special because it is the universal blood type, meaning that it is the preferred choice for blood transfusions. This is especially true when the recipient’s blood type is unknown or in the case of an emergency when there is no time to test the recipient's blood group.

O negative blood is also the safest blood for transfusions in immune-deficient newborns, and it has the lowest risk of causing severe reactions for most recipients.

Because O negative blood is highly versatile, it is in high demand.** However, people with O negative blood type can only receive blood from O negative donors.**

https://www.medicinenet.com/what_is_special_about_o_negative_blood/article.htm