What version of OS are you running? Are you postively sure you have your security and privacy settings updated since the release of Catalina? Have you updated your settings in your System Preferences > Security and Privacy > Privacy > Full Disk Access, Files and Folders, Accessibility... make sure that Lightroom is checked on each of these - if it isn't in the list tap the plus icon and add it.
Im pretty sure the permissions are set to allow write on the destination folder..
Not sufficient for you to be "pretty sure". Please confirm the permissions by looking at them and setting them appropriately. Sometimes they get changed accidentally. Also please make sure the Destination Panel has selected the desired folder and not some other folder where you don't have write permission. Sometimes the Destination Panel gets changed accidentally.
If your OS is MACOS, Catalina or newer, have you inspected for application rights?
Outside of LrC, on the MACOS, bring up System Preferences, select Security and Privacy, select Privacy. scroll down to Files and Folders, make sure Lightroom Classic, and while you are at it, Photoshop, can access all Volumes and Folders