SUMIF - Sum up all the total number when no specific criteria selected

Think you need to explain more.

"when no criteria selected"
So what method do you use to select criteria?

Attach a sample spreadsheet with expected results, remove any sensitive data, create a mockup example if necessary.
Use the Go Advanced option at the bottom of the page then scroll down to Manage Attachments as the "paperclip" method does not work on this forum.

Supply the reuslts of what you expect as your description is not that clear of what you want.

Agree we need more info. Your formula, as shown, will combine the totals, not add them (20 and 20 and 20 will become 202020 not 60)

I suggest that you upload a small (clean) sample workbook (not a pic) of what you are working with, and what your expected outcome would look like.