This is, imho, not the tbl_summary() problem itself, but the bigger issue. The problem may be caused by some character(s) - probably Unicode - which can arise if the file is produced by software using different encoding system and then imported to R (however I can not be sure without the reprex).
Here is a similar thread: R: invalid multibyte string
for instance, you can use Ram Narasimhan's function to find offending character and remove/convert it. Alternatively you may open your file in the text editor and change encoding/delete whitespaces etc..