I freely admit, I’m a nerd about textbooks, but am also bad at using them consistently. Hopping into immersion early was one of the things I wanted to do - definitely had some mis-steps along the way, but that’s totally okay. I have a love hate with Anki - you can style cards to make it look prettier, but I still don’t enjoy using it - it can help you get vocabulary into your head - I don’t find SRS helpful for grammar, and that’s usually the stumbling block to engaging with native material.
It’s helpful to have a basic sense of how Japanese sentences work before you try to immerse, especially if you don’t have much background - mainly because the order feels super backwards to English speakers. There are video series’ out there if reading a book isn’t your jam - Cure Dolly and Japanese Ammo with Misa are both popular (disclaimer, haven’t used either). At the beginning, I would be watching the video/reading the section, and just taking some time to think about it and take away what you can. Fuzzy understanding of the concepts is fine - more exposure will make them clear. Some people like to take notes, some people are more on the train of ‘I looked it up, I thought about it, I kinda get it now, and next time I see it, I’ll look it up again’ - I have been both of those people - they’ve both more or less worked. Particularly as a beginner, most of the grammar you learn you’ll see everywhere and your brain will eventually get it.
I am partial to reading as your first immersion activity because you have lots of time to look things up and figure them out - when I started I really couldn’t look anything up from an anime because I couldn’t identify the words being said at all (better now, but still rough) and hadn’t found any Japanese subtitles yet. The Comprehensible Japanese youtube channel is a nice fit for total beginners who would rather do more listening - you need very little knowledge to get through the complete beginner videos, but it gives you some basic sentence structure and vocab.
Best wisdom from @ChristopherFritz - your first immersion/native content experiences are more puzzles and less “consuming content” - you move through it slowly, look up lots of stuff, and have lots of questions. You will need to look up way more things than you’ll memorize on the first pass - take note of the things that you see often and focus attention on figuring those out - your brain is good at patterns, you’ll start to get that ‘I’ve seen this before’ feeling to cue you to spend some more time on that piece of grammar/vocab. If it’s the first time you’ve seen it, it’s okay to just look it up quickly, get a rough sense, and move on. There’s a bit of a balance between ‘just pick out what you know’ - great reinforcement for your current knowledge, but (to me) less helpful for learning new things - and looking up everything and writing them down. If I wrote everything down, I would not get through much content - I go for quantity of repeated exposure instead of detailed remembering from each exposure. Look up what I need to understand, think about anything new/tricky, continue reading and repeat. Reading can act as SRS for common grammar - you get repeated exposure, spaced out in time.
For some “handholding” in early immersion - you might look into the old (or current) Absolute Beginners Book Club or Beginner Japanese Book Club picks. They’ve taken on a variety of manga/children’s books, and club picks have community completed vocabulary sheets for reference, along with threads where people post questions and get explanations - the community aspect can definitely make reading along easier, and it’s nice to have people around to answer your questions when you can’t even figure out what you need to look up.
It’s okay to try different strategies to figure out what works for you. There may be an ‘optimal’ way to learn Japanese, start immersing etc, but in reality, the ‘optimal’ way for you will be the one you can start and stick too.
Good luck, and welcome to the community