Certificates are not trusted on Chrome and Safari on old iMac with El Capitan

[Nummer378]

@Ella

Not sure if you saw this but my Mac works now after doing it!

Set the DST Root CA X3 to "Always Trust":

Directions for fix:

1. Open ~/Applications/Utilities/Keychain Access.app
2. From View menu select "Show Expired Certificates"
3. On the Left Sidebar pick System Root
4. In search bar top-right type DST
5. Double-click "DST Root CA X3"
6. In pop-up, turn down "Trust" arrow and set "When using this certificate" to "Always Trust"
7. Close the pop-up and put in an Administrator user/password info.
8. Close all open Browsers & Keychain you should be good to go after that.

Just advising that this approach (which effectively means to just ignore the expiry of DST Root CA X3) will only work for a few years. When the cross-sign of ISRG Root X1 expires, this will no longer work. A more future-proof approach would be to include ISRG Root X1.

Trusting ISRG Root X1 was explained by @Ella here:

@Ella

Here's how to fix it. Go to the link below and then down to Mac OS and download the ISRG Root X1 certificate .
https://meta.wikimedia.org/wiki/HTTPS/2021_Let%27s_Encrypt_root_expiry

Once you download that file, go on your Mac to Applications>Utilities>Keychain Access.

• Once in Keychain Access select the System tab on the left.
• Select + on the bottom of the window to add the ISRG Root X1 certificate.
• Once imported, double click that certificate to open it.
• Select the arrow by the Trust tab to open it and change to 'Always Trust' under 'When using this certificate'.

This worked for me, I hope it works for you. Please do let me know if it worked or you're having any issues.