One of lessons learned from the Mandela effect is that there is no limit to anything and that all possibilities are open.
The past, the present and the future could all be happening now. Everybody alive could be the same one person and each lives in their very own dimension inside one global variable dimension. Time is not a straight line and if you could go back to the past, you wouldn't be able change the future, because of the infinite possibilities, dimensions, parallels and versions of yourself and everybody, and that what will happen has already happened, is happening now and will happen again.
Countries themselves could very well be existing in different dimensions of their own and that causes the differences between nations, which are not due to cultural differences, but dimensional differences separated by borders of mass consciousness.
There could be infinite mini-portals scattered around this reality in unexpected areas, so if you walked down the street and found yourself in an unfamiliar place, or a place that didn't exist before, or a familiar place and time you can't remember, then you could have entered one of those scattered temporary mini-portals. Google Moberly–Jourdain incident.
Therefore, regarding the Mandela Effect, the possibility that we may have already moved to parallel universes/dimensions whether naturally or not shouldn't be ruled out.
I classify the 20th century decades after early 1950s into dimensions, not as a cultural, civilizational or social change. We may have experienced more than one dimension shift after WWII. I noticed, for example, that people's heads used to be square until early 1950s, then turned into what looks like building blocks. If you look into the 1960s, 1970s and 1980s separately, the difference will be strange as if each decade exists in a whole different world/dimension of its own. it is not a matter of only changes of costumes, culture or way of life. That isn't the big picture. No matter what changes existed in the 1920s, 1930s, 1940s and early 1950s, there was a kind of dimensional link. The changes didn't feel out of place. The 21st century seems like a parody of the 20th century, recycling stories and material. It is not granular and contiguous.