Unable to use Bootable USB to Install macOS on MacBook Pro

How did you create the "bootable" USB?

Did you follow the guidance exactly as Apple has provided it here?: Create a bootable installer for macOS - Apple Support

About Startup Security Utility on a Mac with the Apple T2 Security Chip - Apple Support

❝Full Security

Full Security is the default setting, offering the highest level of security. This is a level of security previously available only on iOS devices.

During startup, your Mac verifies the integrity of the operating system (OS) on your startup disk to make sure that it's legitimate. If the OS is unknown or can't be verified as legitimate, your Mac connects to Apple to download the updated integrity information it needs to verify the OS. This information is unique to your Mac, and it ensures that your Mac starts up from an OS that is trusted by Apple.❞

Internet Recovery Mode is fine too, but you will need to figure your network issue....unfortunately that can be very difficult to figure out since Apple's error codes don't really provide any clue to the specific issue. It is also possible the T2 chip on your laptop has a problem so you may need to try a DFU Firmware Revive (or possibly Restore, but after a Restore, then Internet Recovery Mode is the only option for reinstalling macOS again):

How to revive or restore Mac firmware - Apple Support

Usually when people are reinstalling the OS it is because they are having issues with their computer. What issue are you trying to resolve by reinstalling macOS?

There is also a good chance the Logic Board on your laptop is bad which unfortunately is a common problem with the MBPro 16" (2019) model.

Yes, I'm sure the Apple Store could take care of it.

Meanwhile, if you're inclined and if you've been attempting the network recovery via wi-fi, you might try connecting the laptop directly to your router with an ethernet cable. It would require an ethernet adapter and cable for that computer, something like this:

USB-C to RJ45 Gigabit Ethernet adapter

Normally to be able to select a boot drive on startup you hold down the Option key and press the Power button, keeping the Option key down until you see the selection screen. If your Mac won't give you an option to select, then there may be a hardware issue with your Mac.

A 2100F or similar error usually means that your Mac can't connect to a reliable network.

Regards.

I agree with @varjak paw. It's possible that the startup drive is failing or failed in this machine. If the Mac can't identify or access the boot files stored on the drive, then it can only default to internet recovery.

Why are you trying to reinstall the OS? Were you having some problem with the laptop?

What was the year & model of the Mac that created the bootable USB?

and DID you manage to use recovery to change the settings to allow startup from an external drive (like the bootable installer) ??