Write permissions on a new encrypted partition
I assume this happened as you have used the partition on Extended Journaled
Open the finder, find the drive under ‘Devices’, then right-click and select ‘Get Info’.  A dialog box should pop up and display the basic info of the drive. At the bottom, there is a collapsed menu for ‘Sharing &amp; Permissions’, make sure your username has read and write permission, and check &quot;Ignore ownership on this volume&quot;

If you are unable to do this , then first try to disable Journaling, and do the previous step shared above
Open Disk Utility, Select the partition and then hold down the alt key. Select the file from the top menu and you will then see an option to ‘disable Journalling’