Custom Table Format won't let me change font color or size

I want to create a custom table format that will automatically set the Font Type and Font Size to match the selected table in the picture below (not the fill colors). So the row and column headers would be Aptos Narrow, 11pt, the data (numbers) would be Aptos Narrow 16 pt, and the top left cell would be Times New Roman 10pt with a diagonal line (All cells centered vertically and horizontally with text wrapping on).

The selected table has various font sizes, I want to create a table style that looks like that.

When I open the New Table Style menu, and select any element to Format, the "Font" and "Size" menus are grayed out and won't let me change them. The second picture shows this.

I can't change the font or size.

Is there a setting somewhere that I accidentally locked table styles to a default font?

I am using the Microsoft 365 version, on Windows 10. I have the "smart features" turned off (so no autosave or "help" button).