Just promote DANE. You could even use self-signed certificates considered as trusted because they are set in a DNSSEC-signed TLSA Resource Record for a host, protocol and port. Unfortunately, end-user software adoption is not the best currently.
I wish libui-ng or even a direct minimalist native controls appeared, but most of them just recreate them and usually having accessibility issues, high DPI, etc. Slint default font looks different on Windows, so the Fluent style does not seem to use the native ones. It looks promising anyways.
Just promote DANE. You could even use self-signed certificates considered as trusted because they are set in a DNSSEC-signed TLSA Resource Record for a host, protocol and port. Unfortunately, end-user software adoption is not the best currently.