Find out using
import matplotlib.font_manager print(matplotlib.font_manager.X11FontDirectories)
On my Ubuntu 22.04, this lists:
['/usr/X11R6/lib/X11/fonts/TTF/', '/usr/X11/lib/X11/fonts', '/usr/share/fonts/', '/usr/local/share/fonts/', '/usr/lib/openoffice/share/fonts/truetype/', '~/.local/share/fonts', '~/.fonts']