..greetings nishantmathur:
There's quite a few relevant topic articles online about this issue in
relation to Certificates, Security; and finally Expiry, on 30 Sept 2021.
These require some deeper reading, since they say more than one thing at a time.
Such as the following; suggests the symptoms affect a certain vintage/version of
macOS; while actually same effect appears to cross all systems, without boundary.
And this article pre-dates the current reality; stated days before
that realization sank-in to the degree/depth it now has meaning.
• El Capitan and older Mac OS X are about to have a security certificate problem | The Eclectic Light Co.
https://eclecticlight.co/2021/09/21/el-capitan-and-older-mac-os-x-are-about-to-have-a-security-certificate-problem/
"This certificate expiry doesn’t only affect older versions of macOS."
"Versions from 10.12 (Sierra) to macOS12 beta (Monterey), and all recent
versions of iOS & iPadOS may refuse to load an affected site, claiming
that their intermediate and root certificates are out of date, despite the
updated root certificate being present. ~ Full details are in this article,
which explains what you can do to address that. This not only affects
Safari, but also third-party apps which use parts of WebKit to connect
to websites."
Highlighted article above, goes past here; other parts
are included by their source(s) with blue-linked text.
• Why won't Safari open that web page? | The Eclectic Light Co.
https://eclecticlight.co/2021/10/01/why-wont-safari-open-that-web-page/
And explains why if you also have & use Firefox, that can work when Safari
and other webkit browsers (which share certain similarity) fail to fully work.
[This not only affects Safari, but also third-party apps
which use parts of WebKit to connect to websites.]
• Apple security certificate issue – MacInTouch
https://www.macintouch.com/post/18319/apple-security-certificate-issue/
"Whether you’re running a server which relies on Let’s Encrypt* certificates,
or trying to connect your browser to one, the most helpful and information
page on the subject is this one from Certify The Web." ~ eclectic light co.
*reason, explained in full detail by Scott Helme, "is that a widely
used root security certificate, that for IdenTrust DST Root CA X3,
will expire in just over a week, on 30 September. This is relied on
by Let’s Encrypt security certificates." -- this also affects newer ones!
Most/all of those Safari 15.0 issues, along with Catalina/BigSur issues
can trace their core issue(s) to these certificates' expiry. Without an
adequate preventative measure, to sustain 'secure' access to internet.
These bits and pieces are why some have been "getting not secure"
errors; the underlying certificate(s) can be patched; while altogether
are kind of a mess right now. Other browsers also will need attention.
"There will be exploit patches for all Chrome, Brave, etc.." [article ]
https://www.macintouch.com/post/18375/
This same factor can unhinge most browsers out there.
Link within this thread proposes similar site/link also posted
similar reply by Leroy in ASC that seemed to work, 4 days ago.
Evidence is, there are 'like-thoughts toward a cure' in this regard.
• Safari update 15.0 not working with any banking websites - Apple Community (20 Sept 2021)
https://discussions.apple.com/thread/253161344?answerId=255997091022#255997091022
reply cited from above:
Oct 1, 2021 5:36 AM in response to appleviv
UPDATE: the fix from user WMendi WORKS :
"If you google "Latest update 10.15.7 with Safari 15.0 that won't load pages",the results
will include a popular Mac related website has a useful user forum that has a solution.
"This fix is a link to download and reinstall Safari 15.0 for Catalina If you have this
problem with a different OS version, you will need to find the correct installer."
..little surprise ~ same workable 'linked' answer appeared in ASC over ten days ago..
While I've been content to run older macOS with ESR Firefox custom build browser.
Good luck & happy trails!
🌤🌻🌿⛵️🎣🐝🙈❄️