mime types of office template files are wrong determined

[o815]

Using current wp 6 public release file uploads for office templates like
file.dotx
another.xltx

are not possible because wp core is making false detection attempt

test.dotx = WordPress recognizes that the file type is [application/vnd.openxmlformats-officedocument.wordprocessingml.document].

false because: this mime type is for docx

test.xltx = WordPress recognizes that the file type is [application/vnd.openxmlformats-officedocument.spreadsheetml.sheet].

false because: this mime type is for xlsx

test files where created with an empty page in word and excel saved as template file in the save as dialog.

[costdev]

Hi @o815, welcome back to Trac! It looks like we're tracking this issue along with similar in #40175. Let's continue the discussion there.