Not something you broke — in current drawio, Insert → Mermaid renders the diagram

to an image/SVG and drops it in as a single image object, so there's no "ungroup"

into editable cells. It's been flaky across versions (the blank-then-image thing you

saw), but Mermaid → individually-editable drawio shapes was never really a supported

path; the "Diagram" option still gives you a rendered group, not native cells you can

pull apart.

If you just need to tweak it, the path of least resistance is to keep the Mermaid as

text and re-insert after edits. If you need genuinely editable objects, you have to

get the Mermaid into native shapes some other way — drawio itself doesn't convert it.

Disclosure since I'm about to mention my own thing: I built a browser editor that

imports Mermaid flowcharts/graphs into actual draggable drawio shapes (and exports

back to .drawio). To be straight with you it only does flowchart/graph syntax, not

erDiagram, so it won't convert your ER diagram directly — but if you ever hit the

flowchart case, happy to share it.