A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Dear Prathamesh Suresh Ch,
We appreciate you post back and share with us these detailed information. And we appreciate your precious time doing tests.
From the screenshot you shared, we can see that there are 51,319 files in the folder. Considering that same situation appears in different browsers, we're afraid SharePoint is getting throttled.
According to this article Manage large lists and libraries - Microsoft Support
SharePoint has 5000 items threshold limit. If a library or a list view shows more than 5000 items, you may run into a list view threshold error.
Therefore, we recommend you refer to the information in same article above to manage your SharePoint library and then upload the folder.
If you need further help, the best way to help you troubleshoot the situation further is reporting it to the related team and let them remotely checking the scenario on your side.
Thus, we sincerely recommend you contact your Microsoft 365 administrator, follow steps in this article to raise a support ticket and contact related team. The support team has higher permission to remotely assist you, they will involve more resource to help you find this issue's root cause and look for solutions. This would be the most efficiently way in handling this case for you.
For reference: How do I find my Microsoft 365 admin? - Microsoft Support
Thanks for your cooperation and understanding!
Hope you are keeping safe and well.
Sincerely,
Tina | Microsoft Community Moderator