>Can I realistically make an app as a junior dev?
Most senior devs can't make a complete app from scratch - and that's not a bad thing. Like most disciplines we specialize, and so a "full stack senior dev" ends up being very good at a small slice of the whole software production pipeline.
Even with LLMs, it takes a lot of effort and iteration before even a small product can reasonably serve a broad group of people.
Don't worry too much about "architecture" - there's never a perfect architecture. I think what you're describing is judgement. Senior devs aren't born with good judgement, nor do they acquire it by solely consuming content (books, videos, posts). The most successful pattern I've seen is: try your best, consider how difficult it would be to change things later, and favour simple solutions in general.
Since you're using this project to learn, I would advise you to use Claude Code with intention. You should read code 10x more than you write code (it's okay if Claude does the writing). Try to avoid asking Claude to explain the code to you. It's nice if you need a quick verification, but generally just try to find things out for yourself.
You're on the right track. Good luck!