OK, it is terminology getting in the way. You want to make a new canvas (aka file) not a template using a pre-set from the drop down menu but for some reason it has gone.
That is a bit strange but not unknown, the standard default configuration files are held in
C:\Program Files\GIMP 2\etc\gimp\2.0 and are copied over when a new profile is created. You can
copy the templaterc file over yourself.
Attachment:
templaterc.jpg [ 158.27 KiB | Viewed 1966 times ]
Replace the existing file. More worrying is why you have lost the contents of the existing templaterc file.
Edit: Just in case the default templaterc file attached. Unzip it. It is just a rather long text file containing all the parameters.