This used to be fairly widespread a long time ago. There used to be fares that are restricted for sale only in a certain country's POS (I believe these are still alive in ATPCO) but not really used anymore.

I remember examples of round-trip ticket A-B-A costing $x in A, $x/2 in B (plus another fare for country C) for some city pairs, but I don't think this has really been a thing in a decade at least.

Are you only just finding out about dynamic pricing? It's still in full swing everywhere. If you want to witness it, the Chinese websites Temu & AliExpress experiment with this on nearly every item. Flights are exactly the same, and because you haven't experienced it shows you haven't caught it