I'd like to increase the font size of the table headers in the BOM. Editing the font size locally does not help. Changing the document settings doesn't help either. The font size of the table title and the items below change, but not the column headings.
If I add my own column, I can change the size of the header, but not in the original one like QTY.
(...) That will expand the toolbar for options to change the font, font size, make bold, etc.
Changing the font in the toolbox doesn't works for headings. I've already tried it.
Notice the icon on the far left of the toolbar. It's dark, which means the row is using the default font.
I changed the default font too. It changes the entire text of the table, but not the headings.
It works just fine for me (see below). If your changes apply to the whole table then it sounds like you had the whole table selected, and not just the header row. Did you click on the little blue box at left of the row to select just that row before changing the font?
Click on the table to select it, then click on the little blue box on the left side of the row. The toolbar shown below should appear.
Notice the icon on the far left of the toolbar. It's dark, which means the row is using the default font. Click on it. That will expand the toolbar for options to change the font, font size, make bold, etc.
If this is something you will want for future BOM's you can right-click on the table and save it as a table template, then you can select if when inserting new BOM's.