Social media searches are common on candidate screening nowadays. Say you left a conservative-sounding comment (like noting that the fast vaccine deployment is due in part to Trump's Warp Speed program) here on HN.

This would be a huge red flag against you when seeking a job at Silicon Valley companies - which are notoriously liberal leaning. "Cultural fit" is what they are looking for, not diversity (of opinions).

Canceling can be something that hasn't happened yet. All that we write online is forever.

Exactly