Mac excel chart-display bugs

I have two problem with chart display in Mac Excel 2021 Home and Student, 16.68. Running MacOS 12.6.

1. Charts frequently display as blank, and when I use Select Data for the blank box, it's empty — no data series therein.

What's especially odd: the chart will come back, both the display, and series in Select Data, reappear.

2. A. The line colors in line charts change randomly when I close then reopen a workbook. B. Some lines (and their data series) just disappear. 

These threads:
https://answers.microsoft.com/en-us/msoffice/forum/all/line-colors-in-excel-charts-do-not-stay-the-way-i/963adf67-e10e-4633-becd-44ae3a382b83
https://answers.microsoft.com/en-us/msoffice/forum/all/line-colors-in-excel-charts-do-not-stay-the-way-i/963adf67-e10e-4633-becd-44ae3a382b83

...suggest that it has to do with an obscure setting:

"Properties follow chart data point."

This is supposed to be under File:Options. I have no such choice on the main File menu, and there is no File menu on my ribbon. Also don't find any such setting in Excel:Preferences.

Any help much appreciated. Thanks.