You can add different types of key to the bitlocker volume. The Windows GUI is limited.
Also the terminology is somewhat confusing and ambiguous. (External Key file, recovery key, recovery file, recovery key within a recovery txt file. Just be aware of the different key-commands and double check your expectations.)
Please open this in a new tab, it may provide some insights.
Manage-bde -protectors C: -add /?
You will have to update the command to your needs. Please understand the difference between a recovery .txt document with numbers and an actual key file. (*.bek) ("External Key file")
manage-bde -protectors C: -add -StartupKey F:
F: is USB drive.
If the system detects the USB stick, it will not ask for a password and simply boot.
Side note
You might want to enable legacy usb in the bios if your USB stick is not detected at all. You can check if you ask for the F8 boot menu. The USB stick should be listed there.
You may delete the password protector after you have successfully booted up from your USB stick in several ports. (Test is; hubs may misbehave.)
Usb Flash Drive
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