Here is a shortened example based on the screenshots above.
TableHeading03.xlsx (21.9 KB)
It shows the matrix-like form with
a) field-list (recommended)
b) table-list
c) few text/line formatting (field-list)
All three for grid-theme settings (Enketo only) and without (Collect or Enketo), after you adapt the settings.
With grid-theme
a) field list
b) table-list
c) label formatting
Default = without grid-theme
a) field list
b) table-list
c) label formatting
You might remove the outer group labels in the form to make them invisible.
Another example can be found here https://docs.google.com/spreadsheets/u/0/d/159tf1wNeKGRccgizZBlU3arrOM--OpxWo26UvZcDEMU/htmlview?pli=1.
More general hints on navigation visibility can be found here https://github.com/getodk/collect/pull/2764.