Yes. On the Canon EOS R8, the burst rate depends on both the drive mode and shutter type. According to the Canon manual, electronic shutter is not limited to only 40 fps:

• High-speed continuous shooting +: up to 40 fps electronic
• High-speed continuous shooting: up to 20 fps electronic
• Low-speed continuous shooting: up to 5 fps electronic

With electronic first-curtain, the corresponding maximum rates are about 6 fps, 6 fps, and 3 fps.

So you can reduce the electronic-shutter burst rate, but not to exactly 8 fps based on the listed drive modes. Your electronic-shutter options are approximately 40, 20, or 5 fps, while non-electronic options are about 6 or 3 fps.