Works as expected and mimics Cycles behavior.
The patch is a bit hacky: In order to not touch the lower level function,
we search for the active output inside groups (recursively) and the first
valid one is then copied (or extracted if you want) in the previous parent
nodetree. So we recursively extract the output node back to the main
nodetree while preserving the links through the nodegroups interfaces.
This way everything works as expected in gpu tree evaluation and bsdf
tagging.
Fix T61869 Material Output Node Inside Node Group Renders Pink in Eevee
d1a744173e