Is it possible that you imported the certificate in a wrong directory? I'm asking because it happened to me, and then I followed this article (step 6) and it started working: https://techglimpse.com/dst-root-ca-x3-expired-certificate-error/
here are the instructions for installing the new, updated root-certificate-file that is needed, according to "techglimpse." the file's name, from "letsencrypt," is "
isrgrootx1.der."
doubleclick the file to install it and, when installing it, choose "Place all certificates in the following store" and choose "Trusted Root Certification Authorities."
incidentally, the techglimpse article mentions that
up-to-date versions of the firefox browser are not affected by the issue since firefox has its own set of root-certificates, which would be up-to-date.