The nonce that was implemented in MainWP is the standard WordPress Nonce. You can learn more about it on WordPress Codex, including the implementation details: WordPress Nonces « WordPress Codex
If you would like, you can add this code to the end of the admin URLs in the Broken Link Checker extension to enable nonces for it.
Apologies for posting it in image form, but when trying to post the code itself here, I’m getting an error. Probably a security feature.
We have already alerted the developers of 3rd party extensions about nonce changes.