If you're looking for a good 3D engine that is open source there's https://o3de.org/ https://o3de.org/ which is now part of the Linux Foundation and based off o

If you're looking for a good 3D engine that is open source there's https://o3de.org/ https://o3de.org/ which is now part of the Linux Foundation and based off of Amazon's Lumberyard game engine