> Was this irony, or has the world become even weirder?
Nope, it's definitely the latter.
Microsoft released a version of Defender for multiple platforms including: MacOS, Linux, Android and iOS. IIRC there's personal and enterprise editions both linked to 365 through "Microsoft 365 Defender".
I really can't imagine it doing much especially on iOS, it's there for the security checkbox/policy I guess.