Answered question

When you record an HTTPS application with NeoLoad, the NeoLoad proxy will be between your browser and your application. NeoLoad will create auto-signed certificate during the recording. Those certificates can be trusted by the NeoLoad Root certificate.
That means that it's NeoLoad that will connect to your server using SSL protocols. For that reason, depending on the server and NeoLoad configuration it might fail.

Since that "SSL connection error "ERR_SSL_PROTOCOL_ERROR" is too generic, the best to troubleshoot that issue is to manually create your URL in NeoLoad.

Just create your server with the right SSL port and create your page with that request in a virtual user profile.
By replaying that URL directly in NeoLoad, you should get a NL-Network-01 error with a better detail regarding the issue.

For example, if you get "javax.net.ssl.SSLProtocolException: handshake alert: unrecognized_name", the issue is related to SNI extension that is enabled in NeoLoad by default.

In that case, go to <install_dir>\bin\NeoLoadGUI.vmoptions, and replace "true" by "false" for "-Djsse.enableSNIExtension" option. Restart your NeoLoad and try again a user validation of your URL.

If it works, the recording should also work.