More about what it means to be isotropic, but not homogeneous…
Isotropic in this context means from an observer on earth, the universe appears to be uniform. It doesn’t matter what direction we view things. Redshifting is not a function of what direction we view it. This can be possible in a non-homogeneous environment if things are happening concentrically and we are at the center.
For example, imagine a series of concentric circles. Each circle is contained in the next larger circle. All the circles have the same location for the center. Sorta like a cross section of a tree trunk. Let’s say each circle is semi-transparent and have a different color. From the perspective from the center of the circle looking outward, the color would be uniform. However, it is not homogeneous since each circle is a different color.
This is what is posited in the white hole model. Each circle represents the collapse of the event horizon over time as matter is leaving the initial white hole. During the initial state, the event horizon is beyond all the matter/energy of the universe. As the matter/energy expands, the event horizon will start collapsing. Eventually, the event horizon will totally collapse as there is not enough concentrated matter to form a white/black hole.