SSL problems after 29th September

So today many web sites were not working - many 'site not private/secure' messages. In both Brave Browser and Safari.

(Elsewhere I was advised there were some security/SSL changes as of today in some externals systems.)

When I set my clock back 24 hours all worked fine. Set it back to today's date and everything broke again.

Brave had an update released on 28th Sept and since installing it, many sites work now, but many still do not, or do not work properly (images not loading, especially).

Running OS X 10.11.6 and Safari 11.1.2 (No I will not update. OS X 10.11.6 / El Capitan includes the last usable version of iTunes before Apple broke it, AFAIAC. And I'm fed up of Apple changing things every year.)

Anyone else running this older version of Safari and having similar issues?

(Makes me wish, yet again, that Apple had less control freakery and offered Safari and iTunes as separate stand-alone apps not embedded as part of the OS. But that's never going to happen. Sigh.)