score:0

Accepted answer
var solutionitems = solutioninforesponse
  .items
  .where(item => solutioninforesponse
     .groups
     .where(group => productgroupids.contains(group.groupid))
     .selectmany(group => group.items)
     .any(groupitem => groupitem.id == item.id))
  .tolist();

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