Maybe setting this to 3?

# Sets log level for libretro cores (GET_LOG_INTERFACE).
# If a log level issued by a libretro core is below libretro_log_level, it is ignored.
# DEBUG logs are always ignored unless verbose mode is activated (–verbose).
# DEBUG = 0, INFO = 1, WARN = 2, ERROR = 3.
# libretro_log_level = 0