French
Been working on my French for a few years (~B1) and found Wesley's approach to be a really nice framework. I'm not using it 100%, but in general a combo of Duo, podcasts, Italki/tutoring, and a cahier/workbook works wonders.
Certainly enough to be able to wander into r/Quebec or r/France and follow conversations, collaborate with French coworkers (productively, but with errors), etc.
Side note: IMO the old Duolingo tree was better, particularly if you already knew -how- to learn languages (even if you've never retained one). If you put in the raw hours and know what you're looking for, it does stick.
New Duolingo...I think might work well for folks starting from the beginning. The changeover absolutely burned how I was using it, so while it was an important pillar early on, now it's much less so for me.
Using desktop+keyboard, reading it aloud, etc. is a must.
I've been using Duolingo for a while, but I think effective learning needs more than just that daily practice to really get lasting results.
Try and get out of Duolingo mode(law of diminishing returns!) and move to native audio(radio, podcasts, movies, songs) in your target language. Get used to being uncomfortable and not understanding anything at first. If you can make a game/habit out of this, you will make progress in due time(think a few years, not months/days). Search around for "immersion learning". I went into the rabbit hole a while back and learnt spanish but eventually being immersed in the language is the only way that seems to work.