How important is learning about Agile if I want to move to a startup

I am a senior developer (8YOE) at a FAANG company. I have only worked at FAANG companies since graduating. I have never worked at a startup and think it could be interesting to try/learn about. I recently interviewed at some small to medium sized startups (<50 devs) and encountered a few Agile related questions that I didn't know how to answer, such as:

"As a lead tell me how you like to break down Epics and user stories"

or

"Do you have experience as a product owner?"

Guys, what the fuck is an epic. (I answered this question just by talking about how I would break down a project I'm writing a design on) I guess I kind of know what a user story is, but also what the fuck is a product owner.

I don't understand any of this Agile stuff tbh. At my current job we don't really have any processes we do a "sprint" with tasks every couple of weeks but nobody does points or anything it's really just to help others track your progress on your project. At the start of every sprint people just kind of talk about what they are working on for the next couple of weeks, if anyone is not aligned they chat about it. We also have a stand up 2x a week.

Is there value in trying to learn about this stuff before going to a small company, or no? Can I just learn this on the job or is it important enough to actually spend time learning/reading about?

Also, why are things done like this? What is the advantage? I've worked at two FAANGs and neither one really had any sort of work planning process outside of picking up projects related to annual/bi-annual goals for the team/org.

Thanks