Thank you for your inquiry! I can definitely understand how beneficial it would be to include a table of contents block in the Third-Generation editor. At this time, there is no specified date as to when a table of contents block is going to be designed or released, but I have submitted this feedback to our developers.
It is possible to emulate something like a table of contents within the Third-Generation editor. You can use our layout blocks located under the Build tab and choose the two-column layout. You can build on those columns by adding additional blocks within them. For more information on this, please click here. I do apologize for any inconvenience in not having this feature at the moment, but I hope this information helps! Let us know if you have any further questions!
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