I'm guessing it uses it to work out the orientation of the app (portrait, landscape) can you disable rotation in either the app or android system settings.
Might not be the fix you want but hopefully will reduce the battery usage.
My phone is always portrait locked. Incase it wasn't obvious the phone was mostly unused for this on the table. Only about 30-45mins was active use of voyager.
Will look in voyager settings for rotation though.
can you disable the motion permission in the OS settings?
Under AOSP and most customs OSes, no. It's not a standard, exposed permission. GrapheneOS does have a toggle for it, though, and I've found most apps don't need sensors.
Sensors permission toggle: disallow access to all other sensors not covered by existing Android permissions (Camera, Microphone, Body Sensors, Activity Recognition) including an accelerometer, gyroscope, compass, barometer, thermometer and any other sensors present on a given device.