If HAProxy uses the PROXY protocol to communicate with Apache on 127.0.0.1:80 and 127.0.0.1:443 then it must be disables. Find any send-proxy in /etc/haproxy/haproxy.cfg and temporarily remove it. Alternativly send-proxy may already be a variable. Then comment that to disable in /etc/sysconfig/haproxy:

sudo docker pull certbot/certbot
sudo systemctl stop httpd
sudo nano /etc/sysconfig/haproxy

# Comment for certbot docker container
#SEND_PROXY=send-proxy

sudo systemctl restart haproxy
sudo docker run -it --rm --name certbot \
            -v "/etc/letsencrypt:/etc/letsencrypt" \
            -v "/var/lib/letsencrypt:/var/lib/letsencrypt" \
            -v "/var/log/letsencrypt/:/var/log/letsencrypt/" \
            -p 127.0.0.1:80:80 -p 127.0.0.1:443:443 \
            certbot/certbot certonly --standalone \
            -d git.machine-deck.jeffries-tube.at,office.machine-deck.jeffries-tube.at,dokuwiki.machine-deck.jeffries-tube.at
sudo nano /etc/sysconfig/haproxy

# Comment for certbot docker container
#SEND_PROXY=send-proxy

sudo systemctl restart httpd