postgres add object to jsonb array from the same column

We want to create a new column where it's a combination for several column as a jsonb object.
ADD new_arrays_col jsonb DEFAULT '[]';
UPDATE items i1
SET new_arrays_col = new_arrays_col || JSON_BUILD_OBJECT(
'col1', col1,
'col1', col2
the new_arrays || ... is kind of like appending to exisitng array with an object. JSON_BUILD_OBJECT is a postgres function to create a JSON object from the parameters