The only path I can recommend is to build a small test project in vanilla JS to get a good understanding of at least its basics, then move to bigger projects such as websites without Webflow. I can recommend Svelte (relatively easy to grasp) or other modern frameworks like QwickJS or SolidJS (a more React-focused approach).
CSS is moving fast forward the last few years and adding new things every month. WF UI options are way behind what CSS can do. Once you will have this knowledge you can move back to WF if you will find it a useful platform for your project.
I didn’t say you can’t rely on jQuery I have only mentioned it because in your code example, you have the script to load jQuery but you do not need it as WF load jQuery on its own.
Web development is a profession like any other and it takes time to learn (same other professions). The only scary part is that it is changing all the time like a live organism. Developing 10 years ago was different than today. Before was everything on Server then all moved to the Client now it moved back s to Server. Modern frameworks I have mentioned trying to find a good balance between what should be served by Server and what should be done on Client etc. etc. etc.
Just keep positive as no one can be always on top of new things.