Currently code.onedev.io does not contain a AAAA record:

❯ dig AAAA code.onedev.io

; <<>> DiG 9.18.13 <<>> AAAA code.onedev.io
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15975
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;code.onedev.io.                        IN      AAAA

;; ANSWER SECTION:
code.onedev.io.         3335    IN      CNAME   onedev.io.

;; AUTHORITY SECTION:
onedev.io.              318     IN      SOA     ns05.domaincontrol.com. dns.jomax.net. 2023032700 28800 7200 604800 600

;; Query time: 0 msec
;; SERVER: 192.168.2.1#53(192.168.2.1) (UDP)
;; WHEN: Tue Mar 28 22:01:03 BST 2023
;; MSG SIZE  rcvd: 128

Returns an SOA, thus the record does not exist.

I am pretty sure all AWS servers come with a huge IPv6 block, a little ask... could you add an AAAA record and make sure whatever reverse proxy you are using is bound to it please.

I would like to one day in the future be able to single stack IPv6 on the web, unfortunately this is going to be a long time, but doesn't mean you cant do a little thing to help the movement :P