When moving files between:

• case-insensitive filesystems: HFS+, ExFAT, FAT
• case-sensitive filesystems: Ext4, NTFS, APFS

LaTeX documents may fail to build if filename case differs from LaTeX code. It’s best to always use lowercase for filenames when sharing with case-insensitive systems.

This example is for the UTF8 package. This stanza works for case-insensitive:

\usepackage[UTF8]{inputenc}  % don't use capitals!

but on case-sensitive systems:

UTF8.def not found from inputenc.sty

Fix by always using lowercase LaTeX package names.

\usepackage[utf8]{inputenc}