I don't think Immortus is a Loki variant. Here's a timeline of the events (past to present to future) of how I think everyone's going down
1. Kang travels back in time and is stuck in a timestorm, appearing in modern-time New York
2. Kang falls in love with Ravonna
2. Kang meets Doom and decides to conquer New York
3. Kang, running Qeng Corp, purchases Stark Tower
4. Immortus (who is an older version of Kang) decides to try and stop Kang from conquering modern-time
5. Immortus teams up with the Avengers and defeats Kang
6. Immortus purges the timeline (hence the ruins of New York being in the void) and traps Alioth in the void, locking Kang "in the future" with Alioth as the guard so that Kang can not travel back in time
7. Immortus invents the TVA, with people from the "nexus event" of the original New York timeline as Minutemen tasked with preserving the timeline
8. To hide his involvement, he invents the Timekeepers as the leaders of the TVA
9. Immortus travels back to the beginning of time for the TVA (3000 BC) to run Egypt as Rama-Tut
10. Ravonna regains her conscious and hatches a plan to free Kang
11. She kidnaps Sylvie and pretends to have her device stolen, and "grooms" Sylvie to go to war against the Timekeepers
12. She sets up for Sylvie to meet with another prime Loki variant
13. When they form a bond, they become the only other being that they won't betray which is why it creates a huge variation in the timeline
14. Together, they make each other stronger, and with two Lokis together they're strong enough to enchant Alioth (which is the spike in the timeline)
15. With Alioth enchanted, the prison that holds Kang is broken
16. Kang is freed from his prison and he begins trying to conquer modern-time earth again
17. Ravonna is reunited with Kang and hands over the TVA to him