The latest Minimal theme version is 7.1.1, maybe updating helps, as this is theme that might provide cover for notes not vanilla Obsidian I think
(I didnt used rendering cover images but did it worked before 1.4? Did it work in sandbox vault?
wikilinks and images aren’t parsed in yaml (wikilinks might be clicable now but as far I know you don’t get an embedded preview of them), and the cover/banner image functionality was provided by custom css or plugins/themes not by vanilla Obsidian, for example here
(but I might missed something)
On my Obsidian
just display image, the same way as
I would say what you requesting is a new feature, not a bug, but devs or others might comment on it (there is no property type “image” that will be be rendered as I read in the release notes)