jQuery "Does not have attribute" selector?

Use the :not() selector.

$('.funding-plan-container:not([data-timestamp])')

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This, by the way, is a valid Selectors API selector, so it isn't specific to jQuery. It'll work with querySelectorAll() and in your CSS (given browser support).

You can filter the selector by using .not() or :not() selector.

$('.funding-plan-container:not([data-timestamp])').

OR

$('.funding-plan-container').not('[data-timestamp]')