It’s just another broken Google Sheets export. Here with .xlsx they don’t write text results of formulas but instead falsely declare them to be numeric 0 values. The best to get around that in this case is probably to download as .ods instead, which seems to be correct on first sight. But Google is also known to fail to export some .ods details correctly. You’ll always have to check what actually works. Recalculation may be your best bet.
The maximum number of columns warning may be due to that several sheets define a
<selection activeCell="$A1" sqref="$A1:$XFD1"/>
sqref AFAIK is somehow related to conditional formatting, or there’s also one sheet with
that’s clearly out of 1024 columns bounds. Note there are 23 hidden sheets, and sheets may have excess formatting applied to far right empty columns as well that may result in this.