I personally only recommend LingoDeer if you plan to take a lot of notes and really practice with the grammar yourself outside of the app. Creating your own sentences with the grammar you learn in that lesson, and things like that.
Otherwise I’d say it’s okay for casual exposure, but pretty rubbish at teaching you grammar that you can recall and use, since it doesn’t expect enough input from the user.
Grammar exposure: yes. Teaching grammar for use: I found it very lacking.
Noooo, don’t tell yourself this! There are a huge amount of resource aimed at very beginners. It’s never too early to learn grammar, because without grammar, any language is utterly useless. ^-^ Get into a learning routine that covers both if at all possible. As someone else already said: take a look at the very long list of resources compiled here on the forum - good stuff there even for people at the very start!