Hi,
with a Nextcloud 21.0.4 jail installation on a TrueNas server i had to replace the jail file
/etc/ssl/cert.pem
here are the commands:
jls 1 sh
sudo su
mv /etc/ssl/cert.pem /etc/ssl/cert.pem.bkp
curl https://curl.se/ca/cacert.pem >> /etc/ssl/cert.pem
hope this help!