There's lots of options for frontend but since you wrote "Mobile accessibility (PWA or native) and having a nice design are a must", there's no way around than digging deeper into frontend / design. I haven't seen a no-code tool (a la Webflow) that translates to good code for larger projects. On paper probably Ionic would fit what you want, but I feel the development experience quite lacking. I'm using Flutter for my mobile apps, and starting to use more and more of Django for backend / full stack (I used to use Laravel, then later Symfony extensively, and they're both still fine options I think).