Hi Sharmila,
As per the detailed description, I understand your demand to export a Visio diagram to PowerPoint. But please accept my apology first that as a community moderator under this support boundary, currently I only have been granted with Visio subscription but no one-time purchase products like Visio Professional 2021.

From my tests, it can be achieved by using the Export to PowerPoint feature in Visio. I attached a test screenshot I made for you above. But from what I noticed in the official article: Create a PowerPoint presentation from Visio - Microsoft Support It seems like the feature is currently only available for Visio Plan 2.
And also, from here: Compare Visio Options | Microsoft Visio It also mentions the PowerPoint integration is only available for Visio Plan 2. In this situation, I may be sorry to convey this feature limitation to only specific version of Visio. And for any urgent work, Visio Plan 2 is available for a free trial for one month where I have highlighted for you.

Also, you can raise the voice directly to the Visio product development team to let them get informed from the real customer requirement to better publish the good features into other Visio versions like Visio Professional 2021. Click: Visio · Feedback Community
Meanwhile, I will keep your thread open to see if there have any community members or MVPs that can share their workarounds or suggestions for your demand based on their experience.
Please correct me if I made any misunderstanding or if there have anything else I can do for you.
Your patience is highly appreciated. Hope you a nice day and stay safe!
Best Regards,
Mia