MS Project: Show ALL Columns / Fields

I know what an Excel column is. But not sure what a field is.
Excel has columns and rows.

So, assuming you mean columns: What columns do you want to unhide or show?

Excel has several thousand columns I do not think you can hide all of them

Look to record a macro in your project to unhide at least one field/column which will provide the basics of what you want. Do you know which fields are hidden? And in what element of the project as there are many parts (views, schedules, tasks etc).

You could then post your code here which will help someone providing a solution for you.

By the way once you hide columns to show them again you would need to insert a column then find the name you have used/created as well as deciding where it should be positioned.