I'm not sure why the Particle app wouldn't show an option for Boron (it does for me on both Android and iOS). Regardless, I'd suggest searching the forum a little bit and think you'll find quite a few solutions here already. From your profile, I see you've read only one post so far. There's a wealth of information here.
You do not have to use the App to set up a new Boron. You will find solutions here on how to exit "listening mode" which is blinking blue. You'll also find solutions for configuring the Boron with the Particle CLI. I for one do not use the Particle cloud at all, nor do I use the app with my Borons. That's your decision whether you want to use them.
There is also code you can flash that will set the Setup Done flag to prevent the device from entering listening mode on startup.
You can always flash your own code by entering DFU mode and flashing from Workbench / VS Code.
Take a look around the forum and then I'm sure you'll be full of questions that members here are very happy to answer for you.