Preview not working in Power BI report builder

Hi,cdBer .I am glad to help you.

It does look very strange.

This is my test.
I tried to create several new Text Boxes, and at the same time change the font size of the fields in the matrix/form (less than 11 pt).
Unfortunately, I did not reproduce your problem (preview/export of paginated reports display text data with different fonts correctly):

 "the text field inserted into the newly created report"

Do you mean the text box in the power bi report builder?

URL:
Add, move, or delete a text box in a Power BI paginated report - Power BI | Microsoft Learn
 

I noticed that you also provided your version information.
this is my report builder version : v15.7.1813.16(same with you)

I hope my test was helpful

I hope my suggestions give you good ideas, if you have any more questions, please clarify in a follow-up reply.
Best Regards,
Carson Jian,
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