Bug
When configuring a datasource's Derived Fields, on only the latest release version, the above toggle is locked in a disabled state.
Expected: should be able to toggle that on and select a grafana-internal datasource that the Derived Field you're configuring should link to.
I can't see anything in the UI to indicate why it would be disabled, and it works like normal on v0.22.2.
Workaround (downgrade)
Workaround pending a fix (if using the Grafana helm chart at least), just set:
https://github.com/VictoriaMetrics/victorialogs-datasource/releases/download/v0.22.2/victoriametrics-logs-datasource-v0.22.2.zip;victoriametrics-logs-datasource
in your plugins array to pin ^
To Reproduce
Run latest of this datasource, grafana 12.3.0 if it matters (that's all I tested), go to datasource configuration, add a row for Derived Fields, click Internal link
Versions of VictoriaLogs datasource and VictoriaLogs backend
VL datasource v0.22.3 (works on v0.22.2)
VL v1.39.0
Grafana 12.3.0