How to preview what Time Machine would back up? I'd like to preview what Time Machine backup would back up if it did a full backup. The UI shows that the backup will be 300 GB but I'd like to understand better what folders contribute to it.

Details:
I use Time Machine with several ignore rules that come from several &quot;sources&quot;:

I ignore some folders manually via Time Machine preferences (the &quot;Options...&quot; button at the bottom of the settings dialog). Those are persisted in /Library/Preferences/com.apple.TimeMachine.plist.
I use tmignore to automatically exclude node_modules and other things I have in my .gitignore files. (Folders excluded this way can be listed via tmignore list.)
Apps can add their own exclude rules, which can be seen by running this command (I'm not 100% sure if it lists everything but that's the command I've used in the past):
sudo mdfind &quot;com_apple_backup_excludeItem = 'com.apple.backupd'&quot;



So I have at least some ways to list ignored files, even though it's not very pleasant that I have to combine several methods.
But even better would be to positively list the files / folder that would be backed up. Those 300 GB most likely contains something that one of the methods above forgot to ignore and I'd like to see what's the biggest contributor to this size. (I used to have a full backup around 100 GB, so there's additional 200 GB hiding somewhere.)
Solution on a terminal is fine, but if there is a GUI app that would visualize that, even better.
Open System Preferences. Tap on the Time Machine option. After having enabled Time Machine and chosen a backup disk, click Options. Click + to define an item that is not to be backed up.