Currently I am using onlyoffice editor with nextcloud integration. But it’s basic to allow only 20 concurrent sessions to edit a file.
So now I look for an alternative and planning to integrate LibreOffice with nextcloud.
So here in LibreOffice any concurrent session limit if I integrate LibreOffice with nextcloud?
You must mean LibreOffice Online. And as mentioned on the page I linked, you would see a warning if you have more than 10 documents or 20 connections in use concurrently. This is to emphasize that an unsupported version is used for something non-trivial.
The warning doesn’t prevent using more connections/documents, it’s just a reminder. However, you are free to prepare your own build of Online without the warning: this is free and open-source product (and naturally, you realize that you are in charge of your modifier instance); or consider using professional support.