Videos won't play at all on my macbook air

Please download and run and post the configuration report from EtreCheck here, opening up a reply here and then using the button that looks like a printed page to get a trxt input window big enough to paste the configuration report here.

I’d expect this is being caused by some add-on anti-malware or anti-virus, or some add-on cleaner, or maybe an ad-blocker, or possibly by some local or network content or policy filtering, but there can be other causes.

After posting the report, boot into Safe Mode, and try accessing the content there. Safe Mode disables various add-ons, disables some optimizations, and rebuilds various caches. It’ll run more slowly, but the content might well play.