Which path you take is ultimately up to you, but personally I would recommend looking for another workplace where the code you work with, the attitude of your co-workers and the astuteness of management better suits what you're looking for in a job. You could stay and try to single-handedly change everything, and while it's not impossible you'd succeed, a much more realistic outcome is you quickly burn out trying to help a bunch of people who are resistant to change.
You said you haven't talked to your managers about it, so that's also an option, but again that could be difficult. You said they love existing staff, so you coming in as a new hire and telling them how crap all the current devs are (given the managers are non-technical and currently everything is "working") might not go down well. Or maybe they'll listen and start pressuring the current devs, and now all your co-workers see you as someone who came outta nowhere and starting messing with the status quo.
The job I just joined, the codebase was heinous, Borderline unusable. And the remote team who had built it was very inexperienced. Luckily I put it to the CEO to remake it from scratch, since it wasn't a huge project, and for me to do it myself, without the developers of the previous abomination (I phrased it slightly more professionally) - and he agreed. And it went great, and I'm happy. But if he hadn't agreed, you better believe I would've been out of there. Not spending 40 hours a week rummaging around in a programmatic septic tank with people who don't share my standards.
Now, you mentioned that the project is relatively new, so maybe making a barely functional mess and doing big refactors or even rebuilds down the line once the project is established and the customer base is there is what the company would prefer - which is a perfectly valid choice for them. But then you'd have to decide whether that's something you'd want to be a part of.
Just as a heads up though - you mention your previous experience is in big tech, and this current one is a relatively new project. If you're referring to a start up, and/or a smaller company, then just be forewarned that this is not an uncommon occurrence in smaller companies and start ups. They don't usually have the standard and regulations and checks and balances and so on that the big tech companies do. In future interviews make sure to ask about what coding standards the company enforces to get an idea if they have anything in place at all - might give a hint to ones that have none and would likely be a mess.