To be able to see custom fields in your grid view, and to be able to search for them, the following information will be helpful to know.
When you are creating the custom field, it is important that you have checked off these settings.
Show values: When this is checked, you will be able to toggle this on and off in the settings, to have it show up on the grid view.
Can search values: When this is checked, you will be able to use the search bar to locate the custom field details.
Can sort values: When this is checked, you allow for the custom field to be sorted alphabetically, numerically, whether an item has this field etc., with the up and down arrows next to the custom field title.