Audition 2020 missing custom effects racks

If you are talking about Effects Rack presets that you've saved, these are stored in a file called EffectsPresets.xml - this is in the appdata section of your user identity if you're using Windows, and it's normally hidden, but it's pretty easy to spot the path when you get in. If you have nothing saved in what's being referred to as 'Audition 2020' (although it's Audition 13 in the appdata) as far as effects presets are concerned, then move the existing file to a new location outside the folder, and replace it with the one from the previous version and they should appear when you re-open the program.

Normally, if it's just a version upgrade, these get transferred anyway upon installation. There could well be circumstances under which this doesn't happen, but I'd have to enquire about that. Oh, and nothing of any consequence to the running of Audition is stored in your Documents folder - that would be far too easy!