How can Migration Assistant transfer less than all files and Apps?

As you may have noted when using Migration Assistant, you can select which things to transfer - as a complete group. The option is not provided to transfer selective files. To do that, you will have to manually copy them and paste in the new medium.

What is the User ( you ) trying to achieve ? Move your content to a new Mac

If the new computer is going to be the Apple Silicon M1 / M2 Equipped Computer - would suggest Only Migrating the User Account and nothing more.

Some have had success and others have been left with a mess when Migrating everything.

1 - Apple Silicon with either Big Sur macOS 11 or Monterey macOS 12 Only Support everything 64 bit and there is no workaround.

2 - Issues that may exist on the older computer will be migrated to the New Computer. This would badly pollute the new Original and Pristine installation of the new OS.

3 -  Applications, extensions and Software Drivers may or may not even work on the new computer.

4 - IMHO - it would be best to only install new application etc Directly from the Developer or the Apple Apps Store.

5 - Due Diligence on New Applications and make sure they are Monterey / Big Sur compatible and factor in the ARMs CPU of the Apple Silicon Computer