For marketing agencies specifically, a traditional is less important as having great evidence that you understand the different levers you can pull to help brands create an identity, understand and message to their customers, foster and grow their businesses, etc. Have you had a customer service job? Had to learn about human psychology by coaching or mentoring? Do you have a well followed social media account or make youtube videos about a topic you care about? Did you organize any events on campus where you were able to use digital or traditional tactics to get the word out? How do you use the internet to get the information you need? What brands do you care about the most and why? If you can answer yes to a couple of these questions and/or have some hard skills like basic web design, managing a Wordpress site, project or event management, etc you might be okay without a traditional internship.
As long as you're able to showcase to future employers that you have unique skills and experiences you've acquired by doing (whether on a job, via extracurricular experience, entrepreneurship, etc) you will have a chance to set yourself apart from the other candidates, whether or not you have a traditional internship. You can always volunteer helping other students with their brand strategies, web page building/design, social media accounts too to gain some real world experience without having to get a formal internship. best of luck!