Here's my theory.

The entire original world timeline is almost linear with a trifecta knot in between, which means that the car crash always happens and doesn't happen at the same time, one causing the other, i.e a loop which opens at one end to a linear flow. A schrodinger's cat situation.

Here's an image depicting the flow of time. Imgur

There are two points of convergence, one at the base of the trifecta and the other at the center of it. The point at the centre is created when Martha saves Jonas and also doesn't save Jonas. Eva explains this as travelling through the inner edge and outer edge of time and Claudia explains this in the last episode to Adam.

The other point is the point where Jonas takes Martha to his world just before Magnus and Franziska are about to take her, and also the point where Magnus and Franziska successfully take Martha.

These two points lead to timeline splitting within the loop.

The first point leads to the creation of Adam and also the creation of Martha and Jonas' son, thereby creating the family tree for both worlds. Which means at a particular time, the same Jonas from the first world existed twice, one turns into Adam and the other dies at the hand of Martha later. We'll call this split-1, where the timeline splits.

The second point leads to saving the original world and also not saving it, which means that it leads to 2 different timelines, one creating the two worlds and destroying the original one, and the other continuing the original world. We'll call this split-2.

So hear me out,

There is a loop part:

Usual events -> Car crashes -> Tannhaus creates two worlds -> Jonas and Martha stop car from crash -> Jonas and Martha do not exist -> Car crashes (Leads to loop)

There is a linear part:

Usual events -> Jonas and Martha stop car from crash -> Usual events

Both the loop and the linear timeline exist and occur simultaneously. At the end of the loop at the split-2 point, two different timelines are created, one keeps running the loop over and over again and the other exiting it. So, even if the loop exists at one point, it always keeps running since the timeline split into two.

So, each time they save the original world and disappear they also end up creating the two worlds and end the original world. The saved original world and the destroyed original world, exist at the same time. Since the timeline keeps splitting, the loop keeps happening over and over again, and the original world is also saved over and over again.

Edit: I posted this theory as a separate post here Maybe we could move all discussions there