Is the external a clone of the internal? If so, how did you make it (SuperDuper, Carbon Copy Cloner, something else)?
FWIW, I use a different desktop background when cloning for a visual confirmation that I'm booted from the clone.
Jon
macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365
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