I’ve reached out to their support about this as well. There are contradicting statements going on, including in Shopify’s support articles.
I’ve attached two photos, ‘Photo 1’ shows the ‘checkout branding’ applies to new customer account pages while ‘Photo 2’ shows that the original statement is incorrect and that the new customer account login page is not customizable. Hopefully, the new customer account login page and dashboard will be customizable soon, but it’s been over a year with this issue and no changes have been made.
In conclusion, customization to the new customer account login page is not possible, nor to the new customer account dashboard page.
