Thoughts on developing SaaS with open sourced code?

Today I heard about how if you use GPL licensing you have to be able to show your entire codebase if someone asks for it.

With regard to how easy it is to just `npm install some-library` and `create-react-app`... I'm wondering if I develop a SaaS should it just be open eg. public repo.

My concern is you're not going to have "obscurity" as a security layer, I'm not saying you should trust that. But when you have your schemas clearly defined, routes exposed, etc... doesn't that mean it's easier to try and break in?(means do a better job)

But I have a SaaS project in mind and it would be pretty complex regarding having multiple-users, real time connection, payments, etc... but thinking about the whole licensing thing.

edit: when I say "open sourced code" in my title, I mean the SaaS code itself that I would develop is freely readable/all of it, down to auth/payment system(Stripe usage).