in the Update Manager under the Edit menu option, you may be able to remove or disable brave in Software Sources possibly in the Additional Repositories tab. i've not used it so it might not show up there.
shows a possible list for the source located at /etc/apt/sources.list.d/brave-browser-release.list
you could try deleting that list if you are no longer using it.
editing to add: that's for mint in the initial section, but the source file should be the same for other debian and ubuntu derivatives. just realized this was the mint section
in the Update Manager under the Edit menu option, you may be able to remove or disable brave in Software Sources possibly in the Additional Repositories tab. This worked and i thank you kindly