Assuming that I have correctly understood what you are trying to accomplish, try the following...

You can create a character style with no formatting added by setting its "Style based on" option to "(underlying properties)." Then apply your character style to all of your heading paragraphs and add { STYLEREF "mycharacterstyle" \L } to the header. For this to work, there must be at least one heading style on each page (otherwise Word starts searching on the other pages).

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional