This happens if the User/password is different. You’ll find the detailed instructions of what to do at BRAVE Sync - ERROR SECURE STORAGE - SYNC DISABLED - #6 by Mattches
I understand you’ve likely already done the MacOS steps, but if you go to the bottom of that you’ll see the steps for Windows users. You may need to default to that, where you go to Sync Internals and clear data, then add the device to sync again.