Reading an .xltx file and Writing to .xlsx file with openpyxl - openpyxl

Question

I've been struggling with this problem for a while and couldn't find a solution else where. I have several excel templates in xltx format that I want to read, then write a new xlsx file after filling in some cells.
Every time I run my code it creates a corrupted excel file. Using a preview extension in VS code I'm able to see that the values were correctly changed. When I read an xlsx file instead of an xltx it works fine. Does openpyxl just not allow what I am trying to do?
import openpyxl
import win32com.client
report = openpyxl.load_workbook("0100048-A5_R_11.xltx")
sheet = report["A5 form"]
search_arr = ["Test_Date"]
for r in range(2, sheet.max_row+1):
for c in range(3,sheet.max_column+1):
val = sheet.cell(r,c).value
if val != None and "$!" in str(val):
sheet.cell(r,c).value = 1
report.active = 1
report.save("output.xlsx")

Answer 1

Copied from the docs:
You can specify the attribute template=True, to save a workbook as a template:
wb = load_workbook('document.xlsx')
wb.template = True
wb.save('document_template.xltx')
or set this attribute to False (default), to save as a document:
wb = load_workbook('document_template.xltx')
wb.template = False
wb.save('document.xlsx', as_template=False)
Although the last line is from the latest docs, as_template is not a keyword argument for save!
This works instead:
wb.save('document.xlsx')