Summary:
Restrict the feature to only show when the reference is a plain link. [i]
This will avoid all circumstances that might potentially result in a deleterious edit.
In the future, we can work on related aspects of the Convert feature to make it more intuitive and accident-proof.
Problem example:
Sometimes when using the Convert button, some information in the existing <ref> is discarded. Before/After screenshot:
See also:
A related idea was split off into:
i. Where, for now, "plain links" means there is not any link-text, just the URL. E.g. <ref>https://google.com</ref> per what @DLynch described in T413279#11519612.
