There is no list.
Don't exclude anything you need to back up.
You don't have to overthink it. iCloud Backup does not back up anything obtained from the Mac App Store, the iTunes Store, iBooks, etc, because whatever you obtain from Apple can be downloaded again free of charge. Those items do not count against available iCloud storage. Refer to What does iCloud back up? - Apple Support.
Apply that knowledge to content obtained from other sources: don't worry about anything that can be dowloaded again. To summarize, back up your work products (almost always stored in Documents), photos (you can use iCloud Photos if you wish), music not obtained from Apple or other downloadable sources... only you can determine what those items are. Email messages for example don't need to be backed up if they are stored on your email service's servers. Messages such as iMessage aren't backed up anywhere other than locally.
Different people will have different backups needs and there is no simple answer to your question. The true test of a backup strategy is to simulate a sudden, catastrophic loss of your Mac and all the information it contains (including perhaps any devices directly connected to it... such as a backup drive). If you can recover from that event with only a minor investment of time and money, then your backup strategy is a good one. If that event fills you with fear and dread, reevaluate your backup strategy.