Mini 5 screen vs. Mini 6 screen is only a little different: 7.9 inches vs. 8.3 inches. 0.4 inches is not dramatic. Yes, one notices if they are used to prior model screens but it is very little change. If Mini 5 felt cramped, Mini 6 will probably feel cramped too. iPad Pro 11 is 11 inches. That will definitely view (obviously) bigger than either Mini. That will be dramatic.
iPad Pro and Mini 6 too are relatively expensive for such simple uses. You might want to look to Amazon or similar for relatively dirt-cheap tablets. Those will have no problem with zoom and movie playback either but cost a fraction of what either of these will cost.
If you had more usage wants and/or some usage was an Apple "walled garden" only usage, you would potentially HAVE to shop only iPad. But for movies and zoom, pretty much any mobile screen will work and all others are relatively cheaper vs. Apple mobile screens. Amazon Fire HD 10 tablet is $149. Refurb: $110. Black Friday will probably turn $149 into about $129 or so.
Yes, yes... sacrilege to suggest anything other than Apple products. But your stated uses are common uses that will work fine on pretty much ANY tablet. Competing tablets cost a fraction of Apple tablets.