My 9-year-old son is gifted. He met the gifted criteria multiple times -- SCAT, WPPSI, etc and scores are pretty high.

He loves Physics and truly understands very advanced concepts, he is fascinated by optics and how the light behaves. I am not saying that as I am an overzealous parent but I truly think he understands it sometimes at even high school level.

He is begging to learn more and I am not sure what to do. I tried some middle school courses on study.com for physics but the problem is he understands the concepts easily but when the equations come or the formulas come he stops and runs away. I think there is advanced mathematics/ algebra which he doesn't like to do.

I am not sure how to nurture his hunger for physics. Any advice will be much appreciated.

Has he ever spent any time playing with the physics (and other) simulations at phet? He might enjoy the interactive, conceptual nature of these.
https://phet.colorado.edu/en/simulations/filter?subjects=physics&sort=alpha&view=grid

He might also get something out of physics enrichment courses designed for grade 7-12 students by MIT students. No homework, no tests, and no math prerequisites. Just interesting video lectures. From the syllabus: "There are no formal prerequisites for this class. However, students should exist in actuality and be located inside a universe, preferably this one."
https://ocw.mit.edu/high-school/physics/the-big-questions/index.htm

The American Physical Society hosts this page for precollege students, with child-friendly articles, activities, and science adventure stories:
https://www.physicscentral.com/

I second AEH’s recommendation of MIT Open Courseware. I was very impressed when I looked at some of their material years ago and recommended them to my DS when he was about the same age as your’s. The thirst for understanding science at a deeper level actually increased motivation to learn more maths in order to be able to handle the formulae & equations.

That MIT open course site looks awesome. I will definitely be checking that out for my space hungry 10yo for science, physics, space and geology.

Also check out these cool physics demos at MIT's Technical Services Group:
http://tsgphysics.mit.edu/front/

And lots of other science videos aimed at all ages of learners:
https://www.k12videos.mit.edu/videos

In addition, there are many intro classes on Coursera or EDX with videos that might also work

Check out "Thinking Physics" by Lewis C. Epstein, and later, conceptual physics by Hewitt.

Checkout "Physics by Inquiry" books and get a little lab for him setup with some basic parts and tools to do simple experiments.

Physics by Inquiry: An Introduction to Physics and the Physical Sciences, Vol. 1 https://a.co/d/7FkX3Pg

Also have him watch "The Mechanical Universe" videos they are really excellent resources that are pretty entertaining and very educational. https://youtube.com/playlist?list=PL8_xPU5epJddRABXqJ5h5G0dk-XGtA5cZ