Is it permissible to keep a computer that belongs to a married woman, which she had sent to my deceased maternal uncle for repair, and he did not return it to her, knowing that it contains her private photos, and given the potential problems that could arise from returning it?

The device should be inquired about from the owner of the device. If she does not have it, or has forgotten it, the device is considered part of the maternal uncle's estate after removing everything belonging to the woman from it. It is not permissible for you to take the device for yourself.