Rather the blame the controller location its could have been with all the improvements that the Mini 6 incorporated that Apple just used a cheaper panel to offset the costs which made the refreshing slower so it was more pronounced on the Mini 6. It was the first year using that new panel size compared to the mini 5.Why haven’t there been lots of complaints about jelly scrolling using the older large iPads in landscape mode then? Or the earlier Minis?
Perhaps the shorter vertical makes it a non-issue?
From a past article about this
Even if Apple has the same specs showing, this many years later they could go with other vendors panel. They have at least 3 different vendors capable of manufacturing this panel size. Whatever specs that Apple requires from vendors could have changed unannounced.iFixit says that it's also possible that Apple is using a cheaper display panel for the iPad mini 6, which could have resulted in the refresh scan being more pronounced than expected.