Based on your descriptions, the attempts, and the shots' results, I can give you three solutions: reset NVRAM/PRAM, boot your Mac in Safe Mode, and boot your Mac in Recovery Mode.
This post will elucidate you one by one in detail to help you fix the Mac not booting from the USB issue and you need to be patient because the repairing process may take you some time.
Solution 1: Reset NVRAM/PRAM
Provided that you have no sureness of whether you have reset NVRAM/PRAM or not, this post explains to you how to reset NVRAM/PRAM literally.
Step 1: Shut down your Mac completely.
Step 2: Press the power button and simultaneously hold down the Option + Command + P + R keys for about 20 seconds.
Step 3: Release the key combination when you hear the second startup sound from your Mac. If it's a T2-based Mac, you'll see the Apple logo appears and disappears twice instead.
Solution 2: Boot your Mac in Safe Mode
You can also give booting your Mac in Safe Mode a shot, which rules out all incompatible software and repairs some errors when the Mac login window gives no response.
Here are how to boot your Mac device into Safe Mode:
Boot an Intel-based Mac in Safe Mode:
Step 1: Shut down your Mac computer and wait for 10 seconds.
Step 2: Press the power button to restart your Mac and simultaneously hold down the Shift key.
Step 3: Release the Shift key when seeing the login window.
Start an Apple M1 Mac in Safe Mode:
Step 1: Shut down your Mac computer and wait for 10 seconds.
Step 2: Press down the power button until the startup options and the Options gear icon appear on the screen.
Step 3: Choose your startup disk.
Step 4: Hold down the Shift key and click Continue in Safe Mode. Then, release the Shift key.
Moreover, if your Mac is T2-based or has an Apple M1 chip, you should also change the startup security settings to enable it to boot from an external USB drive. Or else, you'll fail to boot the computer from the USB.
Now you can boot your Mac from a bootable USB drive in Safe Mode.
Solution 3: Boot your Mac in Recovery Mode
The steps to boot into Recovery Mode on Intel-based Macs and Apple M1/M2 Macs are quite different. You can follow the steps mentioned below according to your Mac device:
Follow the steps below to start your Intel-based Mac in Recovery Mode:
Step 1: Completely shut down your Mac and then press the power button or Touch ID button to power on your Mac.
Step 2: Hold down the Command + R keys together as soon as Mac starts or you hear the startup chime.
Step 3: Keep holding down the keys for a few seconds until you see an Apple logo and release the keys to start your Mac in the Recovery partition.
Step 4: You successfully boot into macOS Recovery until you see the utilities window with a few recoveries and troubleshooting features.
Here's how to boot an M1/M2 Mac in Recovery Mode:
Step 1: Completely shut down your Mac.
Step 2: Press and hold the Touch ID (the power button) for a few seconds until you see "Loading startup options".
Step 3: Click Options next to the Mac's Macintosh HD disk and then click Continue.
Step 4: Enter your admin name and password if asked and you will arrive at the Recovery Mode screen.
Finally, you stated that the Internet Recovery mode was working properly until you encountered an error reading apple.com/support -2100F. I recommend that you check the internet quality directly because the error code appears when something is wrong with your internet.
Take care~
