The key distinction is between obeying a messenger and worshipping the messenger.
The Quran never tells Muslims to worship Mohammad or treat him as God. It tells Muslims to obey him because he is Allah’s messenger (4:80), while repeatedly making clear that Muhammad is a human messenger (18:110) and that worship belongs to Allah alone. As for the claim that Mohammad literally ‘shares Allah’s Throne,’ that is not an Islamic doctrine. Mohammad is not considered a second deity sitting beside Allah.
And “full submission to Muhammad like Allah” is wrong. In Islam, Islam means submission to Allah. Obedience to Muhammad is obedience to the revelation and commands he delivered as Allah’s messenger, not submission to him as a divine being.