Package project: Linux vs LinuxArm64

What is the difference between Linux vs LinuxArm64? Linux - is 32 bit?

I would assume Linux is Intel based Linux, as found in most desktop computers. ARM64 is ARM based Linux, as found in mobile and embedded form factors.

But when in steamworks I set launch options, should I select 64 bit?
And which one should I use when make package - Linux or Linux 64?

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There are essentially no 32-bit Linux targets left that matter.