haproxy tls hash algorithm

The solution for me is: install haproxy 1.8.17 with openssl 1.1.1a from Debian testing. For some reason this combination uses RSA+SHA256 as signature algorithm in the DH key exchange.

The intention was to use the openssl configuration file (/etc/ssl/openssl.cnf) to set the signature algorithm E.g.

[ system_default_sect ]
SignatureAlgorithms       = RSA+SHA256
ClientSignatureAlgorithms = RSA+SHA256

This setting is only available since openssl 1.1.1. But it does not show any effect for me. Anyway, the above-mentioned software combination seems to be sufficient.

I would be grateful if anybody could offer me an explanation for this behaviour.