you don't mention if you have tried a "software" approach to this?

as in : if the hardware "looks good" it's possible that the problem is in the camera's firmware (or, I guess a physical problem with the internals that is not visible)

If you haven't done a "reset" I'd do that, and If you haven't done a "firmware update" I'd do that next (to ensure that it's "all ok"

https://www.support.com/how-to/how-to-factory-reset-a-sony-a7r-iii-camera-11041

https://www.sony.com.au/electronics/support/e-mount-body-ilce-7-series/ilce-7rm3/downloads

if firmware reset / update doesn't resolve the problem, it suggests an internal / silicon-based problem that won't be "repairable" per se - just replacements of the affected boards.... sorry