Does Hajj become invalid for someone who performs Umrah before the lapse of a full year from his Tamattu' Hajj? And is a singular Umrah obligatory for someone who performed Tamattu' Hajj, because the Umrah of Tamattu' does not suffice for the obligatory Umrah?

All that was mentioned in the question is baseless, resembling delirium. One must be cautious about receiving religious rulings from unreliable sources. Once a Muslim completes an act of worship correctly, it does not subsequently become invalid. So, how could Hajj be invalidated by a righteous deed like Umrah (definition)? Umrah is prescribed and encouraged at all times, and it does not invalidate Hajj. The Umrah of the Mutamatti' (one performing Hajj al-Tamattu') suffices for the Umrah of Islam without dispute, and this is a testament to the leniency and ease of Islamic law.