Upgrading from 19.4.x to 20: http2 not working (was probably not working before this version)

[f1-outsourcing]

I was forcing default "Protocols h2 h2c http/1.1". Other websites don't seem to mind. However with Magento 20 I get browser errors

Error code: NS_ERROR_NET_INADEQUATE_SECURITY

If I put back in the virtual host Protocols http/1.1 the shop is working. I don't think this is related to my server setup as other websites show in http2. My virtualhost config for the magento shop is also more or less default. So I suspect it could be settings in the .htaccess file

https://httpwg.org/specs/rfc7540.html#TLSUsage

[f1-outsourcing]

I think it is related to weak ciphers combined with http2. The same server config with http1.1 does not complain, but adding to the virtual host

SSLCipherSuite HIGH:!aNULL:!MD5

Fixes this.

[f1-outsourcing]

could also be related to having a rsa key instead of the ec.