Hi, and welcome.
All you want to know is already answered on manual and forum.
Please use the search function on both.
For your convenience:
audio-pull-up-down-how-does-it-work
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Manual, page 1392:
The ASIO-Guard allows you to shift as much processing as possible from the ASIO real time path to the ASIO-Guard processing path. This results in a more stable system.
The ASIO-Guard allows you to preprocess all channels as well as VST instruments that do not need to be calculated in real time. This leads to fewer dropouts, the capacity to process more tracks or plug-ins, and the ability to use smaller buffer sizes.
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Manual, page 1449:
Activate Multi Processing
Allows you to distribute the processing load evenly to all available CPUs. This way, Cubase can make full use of the combined power of multiple processors.
M1 is a 20-core CPU, so Yes.