This error occurs on default macOS when using software precompiled on another computer, when the person who compiled and released that software has not signed up for an Apple Developer account and submitted the precompiled bundle for notarization, one of Apple's anti-malware prevention mechanisms.
You can usually work around it by right-clicking the app and choosing Open, which usually triggers a special approval dialog. You should generally use caution when doing so, as you're granting an arbitrary binary whose contents you are unlikely to verify access to your private data.
ps. Developers, automating this process as part of your releasing is relatively easy, assuming you have a paid Developer account. The shell script at this link is accompanied by a clear walkthrough, and can be adapted to most workflows run locally on a machine containing your signing keypair. (And if your precompiled binary or bundle was not built with Xcode, you would skip the “xcodebuild” step.)
> “MeetingBar” can’t be opened because Apple cannot check it for malicious software.
> This software needs to be updated. Contact the developer for more information.
Both if I use brew or manually download it.