Makefile spelled with a lowercase "m" don't get a special highlight and color like makefiles with a capital "M". See screenshots below, with problem encircled. The tarball in the circle is the source code of unrar 6.2.2, found here. I wasn't sure if it was just GNU make that responds to uncapitalized makefiles, however apparently all of GNU make, bmake, and kati work for these. I'm not sure if they're standard.

Expected behavior (for comparison)

Problematic behavior

$ exa --version
exa - list files on the command-line
v0.10.1 [+git]
https://the.exa.website/

Operating system: Arch Linux rolling
Architecture: x86_64