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 icon 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.
Checking these boxes will allow you to search the grid view for items in the custom field and also allow you to add the custom field as a column in the grid view through the settings menu.