When I was using Vue (doesn't matter which framework) for Frontend I didn't understand this weird folder structure, I didn't understand how these files are served and how they are built and when I started learning Nuxt which is for Vue Server-Side Rendering, It was weirder for me like how SSR Works, how routes are being generated automatically and how middleware works and this when I decided to learn Node and the reason why I picked node wasn't to understand frontend stuff but to be a Full-stack developer and I was confused what to choose from other stacks like Java or Python or Node and thanks god I chose Node because I was so Lazy to learn a new language and I didn't know that I am so lucky.
Now, I know how NPM Scripts, task runners,building tools and server side rendering work, how frameworks like Vue compile the code I write and I know how to solve problems or bugs that I face in the Frontend part easily or at least much easier than before.
Also, if you are only a Frontend developer learning Node and Express will give you some knowledge about how the backend works and don't worry they are not hard to learn.
Also, Cloud Functions (serverless) will be easy for you when you learn node and some freelancing projects require one or two simple API endpoints like a contact form or counting page views or tracking urls referers...
Even if you don't want to be a Full-stack developer or you are but you don't know Node.js then I think you should learn Node and Express or even take some crash courses for the reasons I wrote above and you might actually change from being a frontend developer to be a backend developer like me.
If you liked this article I am sure you will like this article about why to learn firebase as a frontend developer. Why to learn Firebase as a frontend developer?
I hope you enjoyed this tiny article and this article is about my thoughts and should doesn't mean must :-)