Remove jsonb array element by value

Use jsonb_set() and the delete operator -:

update catalog
set properties = 
    jsonb_set(properties, '{attributes}', (properties->'attributes') - 'is_new');

Test it in db<>fiddle.

So, I believe QRY you are looking for is:

with q as (
  select distinct sku, jsonb_set(properties,'{attributes}',jsonb_agg(el) over (partition by sku),false) new_properties
  from (
    select 
      sku, jsonb_array_elements_text(properties->'attributes') as el, properties
    from catalog
  ) p
  where el != 'is_new'
)
update catalog set properties = q.new_properties from q where catalog.sku = q.sku
;

be aware that I assumed your sku is at least UK!

Your solution works + you pointed me to some new stuff like window functions and give me an idea for alternative solution:

WITH q as (
  SELECT c.sku as sku,  jsonb_set(properties, '{attributes}', jsonb_agg(el)) as new_properties
    FROM catalog c JOIN (select sku, jsonb_array_elements_text(properties->'attributes') as el from catalog) c2 ON c.sku=c2.sku where el != 'is_new'
    GROUP BY c.sku
)
UPDATE catalog SET properties=q.new_properties FROM q WHERE catalog.sku=q.sku;