> For example a new line is valid in a linux file name, but I've never legitimately used one, or do I believe I've even seen one in the last 25 years of using Linux.

Likewise. I wonder if SELinux or AppArmor or the like allows setting a policy for valid filenames to create. E.g. no newlines, only valid UTF-8, only printable characters.

I've seen them (specifically, filenames generated from values in a "modern" configuration language - json or yaml - that mistakenly had newlines in them.) Fortunately, most of the shell tools involved used `-print0` and the related options anyway (because once you have humans involved, it's the easy way to handle normal spaces in names) and the things that did break, where only "some low-value data processing got skipped" rather than anything harmful.