We use Save & Close button while creating a case so basically we are creating and closing the case at the same button.
But I can't seem to find this button in LEX.
Whats the solution here please ?
To close a case in Lightning, you just need to add the status to the Case Status. The documentation notes:
The close case layout isn’t available, but you can add closed statuses to case edit pages. From the Support Settings page in Setup, select Show Closed Statuses in Case Status Field.
You can create a Close Case Quick Action to replicate this functionality. Here is the documentation.