How to block ownCloud folder?

Question

ownCloud/Nextcloud

Everyone knows that ownCloud is good on the server side, everything is poofed.
But on a home car with Windows, everything is in plain sight (except for bitlocker or similar features) that do not fit and I will explain why.
I would like to password the folder so that access to it would be only with a password and + securely encrypted.
But the main thing is without losing synchronization ... clicked on the folder entered the password uploaded the files to the server> closed the folder, and the synchronization would go on and everything would be encrypted on the fly
Any ideas?