update-ca-certificates won’t do anything without a newer version of the certificate collection. You first need to install that .deb file:
curl http://mirrordirector.raspbian.org/raspbian/pool/main/c/ca-certificates/ca-certificates_20210119_all.deb
sudo apt install ./ca-certificates_20210119_all.deb
I wonder why there are no similar reports about Raspbian stretch all over the internet. Guess it’s hard to find because people usually describe a concrete symptom, like here, instead of the underlying problem… 