@John_TN 

I checked the QB_Taxform_Link.xlt file on my computers and got confusing results. For both QB 2012 and QB 2021 (and in 21 even after getting payroll updates) the files indicate that they were digitally signed by a certificate that has been revoked by VeriSign, one that expired in July of 2012. That should mean that they were both initially published before that date, and so they're both very old.

Also confusing is the message you are getting saying that the content of the XLT file doesn't match the extension. I've never seen that message using any of the templates. Normally this should only happen is the XLT file is actually an XLTX file, saved using a newer version of Excel. This is  similar to an XLS file compared to the newer XLSX file format. If you rename an XLSX file and gave it an XLS extension, you'll get a similar warning message.

How that happened - your file appearing to be an XLTX file - is somewhat unclear because none of the templates shipped by Intuit are in the XLXT format internally. The implication is that the template was opened directly by a newer version of Excel and then saved - I suspect by you on your computer.

With both of these things in mind, I don't think I have the same versions of the QB_Taxform_Link.xlt that you're working with, as you're not seeing any of the things I am.

In order to tell for sure why you're seeing different results with the templates from 2012 and 2021, I will need to examine the actual files you're using.  If there's some way you can post them online then I might be able to to that.