Malum wants a mod called "Ortus" to load, but that mod doesn't exist. Lodestone shows up when I google "Ortus", but that doesn't seem to be the correct mod.

Disabling or removing Malum fixes the issue. Updating Malum to Beta 1.4.3.1 fixes the crash.

Log: latest.log

Ortus is the old name for the library mod lodestone. By default the launcher downloads the latest release of lodestone but not the beta of malum, meaning it gets a version that is now named lodestone but with older malum that depends on ortus. Just use the beta instead.

I am, but you should mark it as a release so others don't encounter this issue.