Possible it was set like that intentionally as the options were available to us.
I do not remember exactly, but since 2018 the IPv6 option is being enabled (on one particular domain) always, while the origin host / server is only IPv4 (despite the fact I am running more than 70 WordPress + Cloudflare Websites - no problem).
Also I do not have such an issue as you have with “WordPress Site Health Check/Scan” on WordPress Websites. I also have to admit, neither I use it for any such a useful information - if the Website stops working or throws some error, or something else, I know it immediately without that WordPress integrated feature - but okay, I understand, possibly that’s due to me being myself.
So far, I cannot blame Cloudflare, neither IPv6 - which is being enabled and configured correctly at the origin host / server.
Nevertheless, not having any nor using an AAAA (IPv6) record(s) at the DNS tab (rather just IPv4 - A) for a domain - except the few domains which have got an e-mail service (working fine over IPv6 and IPv4).
Why your web host does not (yet) support IPv6 addoption and developed at his servers/DC, that’s another question (it’s 2021, it passed 10 years already, what are we waiting more?).
Starting today with free domains, IPv6 is no longer something you can toggle on and off, it’s always just on.
Possible, changes in past years or so due to the stated in the below article: