I found that the https://wordpress.org/plugins/luckywp-table-of-contents/ manages to create id's for headings automatically which is nice, and https://wordpress.org/plugins/getwid/ toc block boasts a core like block options experience, which also is nice. Both seems to output semantic html and are easy to style. I'm all for core blocks, as it assures some degree of future support, and hopefully will the core block eventually be as flexible and easy to use as the 3rd party options. Otherwise, I find it hard to understand why you'll want to put it in there?