P.S: Already tried Thunkable: It was too restricted to build an actual app.
When you say “extensive app”, that is a red flag for me.
I would focus on cutting scope and having the app do one simple thing really well. You don’t need an extensive app - you should build something smallerish quickly and iterate on it.
To answer your specific question about the platforms without code, I’m not sure.
Hopefully cutting scope can help you launch quicker (maybe on thunkable) to give you a product to help convince mobile engineers to join your team.
If it is a general purpose application, I'd look at learning rails (this book was great for me: https://www.railstutorial.org/book ) and host on heroku.
If it is an API driven application, I'd look at using a tool like Zapier: https://zapier.com/ or Transposit: https://www.transposit.com/ (full disclosure, I work at Transposit).
There may be some low code/no code solutions for mobile apps, but I'm not in that space so not familiar with them.
Frankly, depending on your app, you could do a lot with google forms/typeform and some manual behind the scenes work: http://paulgraham.com/schlep.html
Again, it all depends on what kind of application you are trying to build.
And if you could give some feedback regarding this that would be great. and I just stumbled on this idea as I wasn't able to find any decent mobile app-building platform which can make things work.