Create a custom type "Diary Entry" and a custom field group "Diary Entry Fields" (see screenshots). When adding a new Diary Entry in the back end (Admin interface), I no longer get the custom field group showing up. I have disabled all plugins other than "Toolset Types", and tried the plain vanilla 2020 theme. All toolset plugins at latest version. Doesn't work with the additional toolset plugins enabled or disabled.
Also, it is not hidden from screen options.
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This issue was previously (erroneously) marked as resolved (presumably because I took too long to see the response). I will keep checking more regularly this time.
My issue is resolved now. Thank you!