Could not create folder “New folder” from admin dashboard of nextcloud
Version we are using is 18.0.3
You’re using an out-dated Nextcloud v18 which has already reached the “end-of-life” state, please update your server to a more recent version (v19-2) asap.
Yes, I know it is outdated version.
But why it is not creating folder’s from admin end?
Why this is happening?
And how to fix this problem?
To be honest, I don’t know and I cannot reproduce the problem because I’m already on an up-to-date version. “end-of-life” means no-one will most likely give you any support on that version anymore which is usually not the case if you’re using a supported version. 
You can still use the search function of this forum to find answers on your question of legacy versions:
https://help.nextcloud.com/search?q=could%20not%20create%20folder
BTW, I’ve never heard that an “admin dashboard” exists in the Nextcloud software where you can create folders?!
Sound like a unix permission issue to me…
All folders have 750 permission and files have 644 permission.
What is need to set for unix permission?
You could try
chmod 770 -R datadirectory
for a test
Ok, now I understand, your speaking about the files app.
It is not only a question of access rights but also file and directory ownership. You should make sure that the owner is always the user under which the web server is running, e.g. “wwwrun”, “www-data” etc.