PowerPoint "groups" alt text not seen by screen reader

Hi,

I am making PowerPoint graphics accessible using alt text. Some of them are charts that are grouped vector graphics created in PowerPoint, so I applied alt text to the group. When I test with NVDA, it reads the text elements in the group, but does not read the alt text. NVDA doesn't seem to read the alt text on any "groups" in PowerPoint.

In order to work around this, I saved a rasterized PNG version of the graphic to use instead, and added alt text to the PNG. NVDA reads this alt text just fine.

Is it okay for me to rasterize these charts? Is there a better way?

I'm worried because I've learned that rasterizing text has some readability drawbacks when it comes to screen magnification. Is it worth the tradeoff? (Rasterizing would also limit translatability...)

Also, does anyone have experiences with other screen readers not reading alt text on PowerPoint groups?

Many thanks for your help,

Brian Stevens