I did study french when I was 19 (today I'm 31), for about 1 yr. But it was a very basic course, just 1 class a week (2h class). After that, I pretty much didn't have any contact with the language for about 11 years. When I decided to restart learning french, I couldn't even remember the difference between the verbs ALLER and AVOIR (go and have, respectively). So, I really think I started from the very bottom. The things I remembered were all super basic, and could be learned within 1 week of study, at maximum.
Regarding the approach: I started using Busuu app. It has 4 levels, A1 to B2, but I just studied up until B1 (I really believe you can't get anywhere close to B2 using any app). The A1-B1 took around 5-6 weeks of daily studies. After that, I simply started consuming french restless: changed the language of all my devices (even my TV!) to french, started reading news only from french-canadian websites, watching a ton of different youtube channels (both focused on learning french, such as Français avec Pierre, InnerFrench and Français Authentique, but also about topics that I enjoy, such as Tesla and Smartphones), and of course, I used Google Translator, Linguee and DeepL probably 100-200x a day (really!). I really don't believe anyone can get to B2 quickly using books or traditional methods. You simply need to immerse yourself on the language. I learned while commuting to work because I was listening to french podcasts, I learned every single time I received a Radio-Canada news notification, and so on.