So Apple now supports booting from externals . . .
Eighteen months ago when I announced my intention to boot my new M2 mini from an external SSD I was met with cries of horror from many who warned of dire consequences.
On a few occasions when I had a slight problem it was hinted that it was a result of booting externally as it was something that Apple never intended.
Lo and behold, we now have a beautiful detailed Apple document describing exactly how to go about it!
Install macOS on an external storage device and use it as a startup disk – Apple Support (UK)
Having been doing it for over a year the only downsides I have discovered are the lack of Apple AI and Apple Pay, neither of which I use, though if I did I would simply boot into the internal SSD.
I've posted this as I feel my actions were justified in spite of the "warnings" and as an encouragement to others wanting to take the same path.
Mac mini, macOS 15.4