How to stop mac from default booting in deleted windows via boot camp?
The NVRAM holds the location of the default OS, so resetting that might get you back to the default search order. If you want to set it explicitly, Apple’s article linked below as well can help:
From How to select a different startup disk:

Use Startup Disk preferences
When you use Startup Disk preferences to select a startup disk, your
Mac starts up from that disk until you choose a different one.

Choose Apple () menu &gt; System Preferences, then click Startup Disk.
Click the lock and enter your administrator password.
Select your startup disk, then restart your Mac.



NOTE: Restart the Mac by clicking the Restart... button. This process checks the system has the correct permissions to start, then writes your choice to NVRAM.