Yes they are no longer scared of the licensing enough most modern Apple devices do have at least some FLAC support.
Also ALAC is a free and open source codec which also has wide support.
And with a tool like FFMPEG you can easily convert between the two and they are both lossless so there is no data lost in the conversion.
So really just use whichever you like it really doesn’t matter.
I think both work since opus is the codec but ogg is the container, but personally I’d probably go with .opus because it’s more descriptive.
Btw Apple’s ALAC and AAC files are typically stored in an mp4 container but with the m4a extension to mark it as intended to be audio only (although it may have a video track, which usually is used for album art).