Suggestions for Tabulate Excel Export Formatting and Multiselect Slicer Settings

Excel Export Does Not Reflect Font Formatting
The main problem seems to be that font specific formatting is not exported even though cell and grid formatting from themes 
Try applying font styles directly in the 'Tabulate' view rather than depending on the font formatting in the 'Themes' on the Design Tab. Choose the cells or columns you wish to format in the 'Tabulate' view. To apply the preferred text styling, use the font formatting options (font type, size, bold, and italics) found in the Tabulate ribbon. This method may increase the likelihood that the font properties will be preserved during the Excel export process by explicitly setting them at the cell level in Tabulate.

Excel Export's Multi-Select Slicer Isn't Working
According to the document, slicers function well for single selections but not well for multi-select dropdowns, where formatting is also lost. This implies that the export procedure's handling of multi-select filter contexts is limited. The distinct discoveries for every necessary filter combination because direct export with multi-select slicers is problematic.
Make Individual Discoveries: Make a new Discovery with the filters applied for every distinct multi-select filter scenario that you need to export.
Tabulate Every Discovery: Put each of these previously filtered discoveries into a separate sheet or section under Tabulate. As demonstrated in your process you can drag and drop these discoveries.
Export the Tabulate View: Export the Tabulate view in its entirety. This will create an Excel file that already has all of the filtered views you want.
By preparing the filtered data in advance this method avoids the live slicer problem during export.