Hi and welcome to the forum:
I don't have an R7, but I have read and researched quite a bit on the subject. To get to use the H and H+ shutter speeds, you seem to need to switch to electronic shutter. At that point you should be able to get to up to 30 FPS. I recommend you review your manual and look specifically for references to shutter speed and electronic shutter.
I recommend you check out this review of the R7 by respected wildlife photographer, Duade Paton:
I think this post actually refers to another thread Bill.
The H and H+ drive modes are available on the EOS R7 when it is in mechanical shutter mode. There are a few things that the camera needs to use the H+ mode. Those are listed on the manual page HERE and I've included them below as well:
H+ enables approx. 15 shots/sec. continuous shooting speed when set to [Elec. 1st-curtain] or [Mechanical] under these conditions.
Using any of the following power sources
Thanks so much for that clarification! 😊
One of the Noise Reduction or Image Enhancement settings restricts your range of available ISO settings at the low end. It might Highlight Tone Priority. Disable all of them if you are shooting RAW.