Hi !
news over here.
the problem was here:
RewriteEngine On
RewriteCond %{SERVER_PORT} !^8443$
RewriteRule ^/(.*)$ https://%{SERVER_NAME}:8443/$1 [L,R=301]
instead of using a rewrite, you have to use a proxy pass, like this
<VirtualHost *:443>
SSLProxyEngine On
ServerName odk.exemple.com
SSLEngine on
SSLCertificateFile /etc/letsencrypt/live/odk.exemple.com/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/odk.exemple.com/privkey.pem
ProxyPreserveHost On
ProxyPass / https://odk.exemple.com:8443/
ProxyPassReverse / https://odk.exemple.com:8443/
Have a nice day and thanks again to the team!