Scene/HDR modes on the EOS M5 generally expect electronic communication with the lens. With a fully manual lens, or with an adapter/chip that only partly imitates a Canon lens, the camera may refuse to fire because it can’t get the lens data those automatic scene modes rely on.

That’s why manual-lens use is most reliable in M and usually Av mode, where the camera does not need full control over the lens aperture. P and Tv may be inconsistent because they can require aperture control or other lens feedback. Scene modes are even more dependent on lens communication, so shutter release may be blocked if the camera does not properly detect a compatible lens.

In short: this is normal behavior for many scene/automatic modes with manual lenses. Use M or Av for dependable operation, and if you’re using a chipped adapter, the chip may not be providing all the information the camera expects.