Solution / workaround.
Changing themes to suit a TOC is impractical and for anyone wanting a workaround I have found a solutiion as follows…
e.g. Where background is white, then
1. change each header font colour to white (thus the header will disappear but still be there (white font on white background means the header is not visible but it is still there.
2. add a paragraph block 1 line down from the header used for each TOC
3. type the header and change the font size or bold to suit your style and make the font colour black (or other colour to suit your theme)
Now when clicking the TOC item it will jump to the white (unseen) header which is above but because you have added another line below that is visible the user will see what they think is the header.
Standard wordpress themes will work without this this workaround but standard themes may not suit your style (there are tens of millions of WP sites are not using standard themes and if some need a workaround for the TOC displaying above or below where it should then this tip may help)
I had testing 3-4 TOC plugins and some work and present differently and well. Good plugins and very useful.
Thanks