Not able to share files or break permission inheritance in Large document library

Hello,

I have a SharePoint site where we have a large document library with 652593 items.

Lately I came to know via users complaining issues with sharing files and breaking the inheritance for special permissions within that library.

If I talk about sharing issue, all the folders are not sharable anymore and I can see different error message shows up while I try to share them

Within the same site, If I create another document library, I can manage special permissions and share files too.

I read about the threshold limit which I guess already surpassed in my case. but how can I manage how many unique permissions I have within this document library?


Can someone please educate me here
Thanks in advance