https://www.peernet.com/creating-high-resolution-tiff-images-for-print/

Sorry; Getting better than screen resolution is usually not possible. If you have the original graphics, use them outside of powerpoint. You could resample in PS. If you do not have access to PS; you can view the slide on the largest screen you can find and photograph it. The camera will "resample" for you. Just download the photo of the graphic.

The attached discussion might help getting high resolution screenshots

https://www.researchgate.net/post/How_to_enhance_paper_Thesis_figures_and_images_Resolution_and_Quality

There are several suggestion in the following link that provides answer to your question

https://www.researchgate.net/post/How_to_save_Powerpoint_figures_as_image_with_300_DPI

The attached youtube video shows how to save high quality ppt figures.

https://www.youtube.com/watch?v=TEFJBeZmsCI

The attached link shows how to export high quality images from powerpoint

https://support.microsoft.com/en-us/help/827745/how-to-change-the-export-resolution-of-a-powerpoint-slide

https://www.peernet.com/creating-high-resolution-tiff-images-for-print/

https://www.researchgate.net/post/How_to_save_Powerpoint_figures_as_image_with_300_DPI

This link provides answer to your question.

Change the registery setting. You can find the instruction here: https://docs.microsoft.com/en-us/office/troubleshoot/powerpoint/change-export-slide-resolution