After being worn down by noip.com confirmation emails, I switched to Google Domains since they include dynamic DNS support with a domain purchase. Google DDNS was easy to set up on my ASUS RT-AC68U with its built-in support. However recently my router was mistakenly bringing down my connection due to DHCP issues so I immediately switched to dd-wrt. Everything about dd-wrt is great... except it has no built-in support for Dynamic DNS over HTTPS/SSL which Google Domains requires!
The wiki pointed me to a curl script however
curl failed to complete the TLS handshake with the error
error:140943FC:lib(20):func(148):reason(1020) which is due to an unsupported cipher. Luckily there is an easy, if less secure, workaround until
curl on dd-wrt is upgraded. Run
--tlsv1.1 to negotiate down to TLS 1.1.
With this change, I have Google Dynamic DNS support on dd-wrt with this startup script and script!
Hopefully you also will be relieved of noip.com emails!