Make series buttons available only after a layer is selected

[DelazJ]

What is the bug or the crash?

1. In a print layout, add a chart item
2. In its properties, "Data Source", "sort by" and "series" buttons can be edited without selecting a layer. You can currently add and configure(?) a series but I can't tell how that actually works, there is no layer fields, thus hard to identify what it relies on.

Unless I miss the subtlety, I think they should be available only after you selected a layer.

Steps to reproduce the issue

see above

Versions

QGIS 3.99 2e07d98

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

No response