Writing and speaking are effective at establishing long term memories, it's why we do it for other things, but a language learning beginner has no idea if what they're writing makes sense or if there's any subtle mistakes in how they're pronouncing words or how they're putting them together, etc.
Language learning experts don't recommend you start speaking/writing unless you have a coach or have reached an intermediate level so that you can discern when something sounds native or not. That way you can self evaluate with recordings, etc.
It is an effective tool for learning, but for self-learning you're gonna be shooting yourself in the foot long term. You should only do it if you have, say, a partner that speaks the language and doesn't mind correcting you all the time.
For Japanese I recommend that you do learn how to write kana/kanji from the start, and even some vocab if you want. But stop there. Don't write sentences, don't try to talk to japanese people on those apps/discord etc. and wait until you're at an intermediate level to do it, otherwise you'll form some very bad habits that are very hard to undo.
https://learnjapanese.moe
https://alljapanesealltheti.me/ (this used to be THE guide for learning)
Using just Renshuu and Wanikani I learned enough Japanese to be able to engage with Japanese content and for it to be actually comprehensible.
In the past I tried learning through immersion only, made no progress, found it demotivating and gave up. You need a baseline of vocab and grammar, and I don’t think it matters much where exactly it’s coming from (apps, lessons, textbooks).