I’ve seen a few issues here with importing Safari bookmarks. The workarounds in those posts work fine (exporting from Safari, etc.).
However, the root problem is almost certainly Mojave and full disk access. Safari’s bookmarks are stored in ~/Library, and that folder is restricted as of Mojave. (Or was it High Sierra? I don’t remember.)
If you want to import directly, you’ll have to (at least temporarily) give Brave full disk access in System Preferences / Security & Privacy / Privacy. The bookmarks will then import successfully. You probably want to remove full disk access after they’re successfully imported.
Or, again, the workarounds in the other posts work fine. I’m just noting the root cause in case anyone is interested going forward.