Hello Surendar Kasinathan,
I'm sorry to hear that you are experiencing issue when you paste link from Excel to PowerPoint slide.
I understand your concern and I'd like to convey that I just did a test in Microsoft 365 Excel and PowerPoint, it works fine, data copied from Excel is pasted in PowerPoint slide.
I notice that you are using Excel and PowerPoint from Microsoft Office Professional Plus 2019.
Consider that we mainly focus on Office issues from Microsoft 365 Business Subscription and I didn't reproduce the issue, I'm afraid it may be a bug or temporarily server-side issue in Office Professional Plus 2019.
Therefore, I recommend you post your concern to the dedicated channel Office Management - Microsoft Q&A members and engineers over there are proficient in the knowledge of Office Professional Plus 2019 queries, they also have the correct escalation channel to escalate this issue to check more from back end. This would be the more efficient way in handling this case for you.
Your understanding and patience will be greatly appreciated. Have a great day!!
Sincerely,
Tina | Microsoft Community Moderator