Issue sharing PowerPoint

My colleagues have encountered a problem that when they go to share their screen to show a PowerPoint presentation, the PPT presentation isn't an option to be selected.

Has anyone else come across this problem? I can't replicate the problem so am having trouble diagnosing the issue.

Both colleagues have said they had the PPT open on their computer ready to go but it doesn't show in the Share Screen dialogue box as an option to be shared.

Any help or ideas will be much appreciated.