Found this here, which fortunately fixed my issue with 3 lines:

sudo mv /opt/Citrix/ICAClient/keystore/cacerts /opt/Citrix/ICAClient/keystore/cacerts_old
sudo cp /opt/Citrix/ICAClient/keystore/cacerts_old/* /usr/share/ca-certificates/mozilla/
sudo ln -s /usr/share/ca-certificates/mozilla /opt/Citrix/ICAClient/keystore/cacerts