From a search:
Extensions not published on the Chrome Web Store may be disabled for safety. You can manually enable them by enabling Developer mode in brave://extensions and dragging the .crx file onto the page.
To prevent users from disabling or uninstalling specific extensions, you can use the ExtensionInstallForcelist policy. This requires manually editing the Windows Registry to specify the extension IDs.
The Developer Mode 3was required to install it in the first place (unpacked) :^/