I’ve learned (I guess still learning) a new language as an adult for the last 2 years. I tried just about every method to learn (classes, courses, books, god knows how many apps/services). To get to the point of being able to accelerate your learning with foreign movies & TV shows, you need to have consumed around 200-400hrs of the language in a comprehensible format first. This is how I would do it if I had to again:
Forget about grammar for now. Grammar is boring and it will make you second-guess when trying to form sentences. Better to just practice and have someone correct you as needed. You’ll learn grammar naturally to an extent (i.e. it will just SOUND right), and you can supplement it later on when you have a better grasp of the language.
Use beginner audio lessons that focus on simple phrases and/or short stories (e.g. Pimsleur or US foreign service language tapes). This is to help train your ear to understand how words are pronounced. This should get you about 40-50hrs of practice.
Find some French youtubers that use the comprehensible input (Krashen) method to complement the audio course - some recommendations in this reddit thread
Once you have around 50-100hrs in, now is the time to find some easy content to consume. My recommendations would be: 1) movies/tv shows you already watched in english but dubbed in french (so you already know the context. You might need to leave off french subtitles if they don’t match audio), 2) podcasts or audiobooks where only one person speaks at a time, 3) french kids shows
After 100hrs, I would continue to consume content as detailed above but you might be able to throw in some easy french-made movies/shows at this point - your goal is to understand about 80%. If you find you can’t understand enough, put it on the backburner to revisit later. You might also be able to read an easy french book now too. You could just reread a book you’ve already read in English but translated in French now (again, so you have context; I read Harry Potter for instance)
Learning a new language at an older age was pretty eye-opening. It’s definitely harder than I expected but it’s so rewarding to be able to connect with a different group of people at a much deeper level, as you also start to understand their culture a lot more, and it gives you access to new movies, shows, theatre, books, music etc. etc.
Good luck on your journey and let me know if you have any Qs!