Guy who is (basically) fluent in his second langauge here. This is how I did it

after achieving a ~B1 level in the language I was learning, I decided to do something that made me go fluent in like 2 to 3 years

I changed everything I do on my phone and the internet to this language. The UI, the videos I was watching, the articles i was reading, the wiki pages, and the conversations I was having with people online. I didnt understand a lot of what of the words i was reading or hearing obviously, but my brain understood what was talked about via the context, and each time it did that, a new word that i didnt know before got added into my volcalbulary. also, by watching casual videos in that language, I developed a native accent over time. it wasn't that easy though, sometimes i got embarrassed or mocked for using the wrong grammar or word. for example, I used expelled when I wanted to say my parents divorced, and used on instead of in multiple times.

[the language in question is english (native tongue is Hebrew). I only used Google translate once (gorshu means both expelled and divorced in hebrew, I only remembered i used the wrong definition of it, so I searched it up) and android auto correct/grammar. you're welcome]