This worked for me with small changes. I found and added two more symbolic links using these commands:
wget -O /etc/univention/letsencrypt/lets-encrypt-r10.pem https://letsencrypt.org/certs/2024/r10.pem
wget -O /etc/univention/letsencrypt/lets-encrypt-r11.pem https://letsencrypt.org/certs/2024/r11.pem
ln -s /etc/univention/letsencrypt/lets-encrypt-r10.pem /usr/local/share/ca-certificates/lets-encrypt-r10.crt
ln -s /etc/univention/letsencrypt/lets-encrypt-r11.pem /usr/local/share/ca-certificates/lets-encrypt-r11.crt
ln -s /usr/local/share/ca-certificates/lets-encrypt-r10.crt /etc/ssl/certs/lets-encrypt-r10.pem
ln -s /usr/local/share/ca-certificates/lets-encrypt-r11.crt /etc/ssl/certs/lets-encrypt-r11.pem
update-ca-certificates -f
I also checked the ownership and the access rights.