You can see that the Attribute table is not visible
The variant section is not visible at all for the Item variant. This is despite the fact that the system acknowledges that this is a valid variant of the template as shown below
On import, I found my most common source of error was a malformed import file that did not comply to field specs (eg. missing reqd field, or incorrect field format). Not to say that this is happening in your case - just something to look at
In the case of imports, it’s mostly trial and error. The other possible problem is the format of your file. In some cases, I found the Excel formatted files didn’t work, but LibreOffice files did work. There are no noticeable differences in the file, but it sometimes works, and sometimes doesn’t.
Might be worth trying it though