UAV Coach is another good online study site. I used them & they work as advertised.

https://uavcoach.com/?utm_campaign=Student%20Newsletter&utm_medium=email&_hsmi=128716715&_hsenc=p2ANqtz-8-R-SpdIt0uplYHiPgGPYYV2hwNPFrXTd6F4xzZ9v_Qne7LTUItPyFsTlWXPm38cv2LL-xW9LFTkclcgsw2UvmSIJ-Ng&utm_content=128716715&utm_source=hs_email

John & Martha King, King Schools, are also now offering drone study course. These 2 people are amazing. I used their private, commercial, & CFI training courses back in the '80s for weekend ground school training. They must have 10,000 didn't courses available. I met them several times & they joined our "large" group at our aircraft camping area at Oshkosh years back. Lots of bratwurst & lots more liquid refreshments were shared every year. Anyway, John & Martha are truly dedicated to aviation. Here's their drone course:

https://www.kingschools.com/ground-school/drone-pilot/