DDNS Certificate Issue

Device: Xiaomi AC2350
FW Version:23.05.0-rc3

I've been trying to upgrade my DDNS from HTTP to use HTTPS connection but so far I've been unsuccessful.

I've got myself a certificate to use:

By using the DNS challenge:

and then tried to export the certificate to my pc and uploaded it to router's etc/ssl/certs location like "/etc/ssl/certs/mycert.cer":

but whatever I do, I never seem to get the system to use it instead of the OpenWRT certificate:

I have libopenssl3, wget-ssl, ca-certificates and ca-bundle packages installed on system.

What you are doing is wrong. The Path to CA-Certificate in DDNS is to be able to verify the certificate of the update server for the DDNS and expects to find the Certificate Authority certificates in the directory.
If you need to add a certificate for the Luci, you can do it in Services -> uHTTPd