No, you cannot get a *real* GED diploma entirely online. While many GED preparation courses and testing *registration* can be done online, you must ultimately take the official GED test at an approved testing center. These centers are physical locations and require in-person attendance for proctoring and security reasons.
There are many online resources that can help you prepare for the GED, but they are supplementary to the in-person testing required to earn the diploma. Any program claiming to offer a GED diploma solely online is likely fraudulent.