Hi,
I've tried duolingo for about 2 months straight and all I know how to say is rice, american, italian, english, water and some other useless stuff, it doesn't even teach you to write or anything like that. It sucks.
I know the best way to learn a language is to go to a teacher or something, but I prefer not to do that and learn it online.
It will probably be harder for me since my native language is not english and I doubt there's lessons or something online for mandarin in my native language, but I'm willing to try, I know english pretty well.
If you like SciFi TV shows, there is a version of The Three Body Problem that's pretty good.
I think you can find versions of pop songs and Christmas songs with Chinese lyrics.
I found it kind of boring myself, but it's head and shoulders better than the Netflix version; it's certainly extremely cerebral and impresses me on an intellectual level, but at a certain point I felt like I'd like to see some cool stuff on screen (still though, easily better than the Netflix version; I couldn't even finish the first episode on that one)
If you want watch/interact with Chinese media then I'd recommend https://www.youtube.com/@MadeByBilibili Many different Chinese animated shows and everything should have english subtitles too. I also recommend watching Ling Cage. It's a cool animated scifi show and it's also for free on that channel and all the episodes there are so far are in one video: https://youtu.be/rqD66LrLYHI