I disconnected my wallet from the partner exchange but still receive a device limit error
Unfortunately disconnecting from Brave's side does not remove the device from the partner exchange's side at this point in time.
There is currently no way for a user to directly and completely disconnect a device to allow another device to connect instead.
For now, if you have reached the limit, you can request for one slot to be freed by following the steps found here.
The Brave team are working on a way for users to properly disconnect devices from partner exchanges instead of the support team manually handling it. [Current November 16 2021]