I just had to learn French in middle age, and it’s been fun. They key takeaways from my experience:

1. Contact is everything. The longer you spend listening, reading, speaking, just in general interacting with the target language, the better. Doesn’t matter what you do - Duolingo or PeerTube videos, novels or comic strips.
2. Communication is the goal, not fluency. You can get the gender of a word wrong and people will still understand you. You can use the wrong tense and that’s usually okay. Don’t try to “sound more like a native” or “learn slang words that everyone uses,” because heaven knows nobody is going to take you for a native. But if you can get the point across and can understand what people are saying, you win.
3. Speaking is 10x harder than listening or reading or even writing, because it involves not only forming sentences in an unfamiliar language, but also saying them, which involves your muscles. At first, it’s really hard to say the sounds of the language that don’t exist in your own language, and I found that very frustrating.
4. Language and culture are different, but interconnected. You don’t really speak a language if you don’t understand the culture it’s attached to. For instance, at first I didn’t know what the cashiers were asking me at the checkout, until I learned that they want to see the bags you brought from home to make sure they are empty. The problem with missing cultural references is that everybody around you knows them, and they don’t understand why you don’t, or what there is to explain.
5. One of the very few great use cases of LLMs is, in fact, talking with a chat bot. You give it a good prompt (look for them online) and you are forced to talk in the target language. If the bot can understand you, a native speaker probably will, too. A good tip is to try an AI conversation on the topic of something you are about to do in real life, like applying for an apartment or having a conversation about cheese.
6. Personally, I found that my language skills drowned completely under certain, specific circumstances. For instance, for the life of me I cannot understand voice messages, at all. Even phone conversations are really bad for me, both in talking and listening. I can have a perfectly fine conversation with someone, but when I have to talk with them on the phone, it’s like I never learned the language.
7. The tool you use is not as important as the time you spend. Duolingo was really meh: too much useless vocabulary, not enough grammar and pattern recognition, lack of ability to specify areas of interest, down to always on animations even when you had them all turned off. But, despite the heavy focus on the words, “chouette” and “trousse,” I sort of learned French to the point where I can follow everyone along and can speak and be understood. Took a year to the day and the entire tree.