Windows Update, ESU, System Restore fail, fill C: drive

My C: drive on my laptop running Windows 10 Home has gone from about 20 GB free to 133 MB free after aborting Windows 11 installation, trying to sign up for ESU and trying several times to use System Restore to put things back the way they were. I'm hoping you can tell me where to look for the leftover files that are causing my C: drive to be so full. Here's roughly what I did, in order:

1. I set Restore Points between the steps below.
2. In Windows Update, chose to update from Windows 10 to Windows 11 24H2. After a lot of downloading, I got an error saying C: was full, that I should attach an external drive and remove about 5 GB from the disk. I tried for a while but realized that installing Windows 11 could fill my C: drive and make the computer useless. So I canceled the update.
3. I read that ESU (which extends Windows 10 updates for a year) requires a Microsoft account to sign up. I only use local accounts because I'm often not on the Internet, and a Microsoft account requires me to be online. I created a Microsoft account with administrator privileges. From there, I ran Windows Update... but didn't see the option to join ESU. Then I went to the local adminstrator account and tried Windows Update again. I don't remember what happened, but I couldn't get ESU. The worst is that this changed my local admin account to a Microsoft account!!
4. I tried System Restore to (I hoped) un-do the change to my local admin account, remove the Microsoft admin account, and un-do the files that were clogging my C: drive. But System Restore failed because there wasn't enough disk space. I tried earlier restore points, but for some reason they had been deleted.
5. I started a chat with Microsoft support, then had to restart the chat after the first reboot during System Restore. The agents ran Disk Cleanup and also cleaned up various folders. That gave me about 3 GB free... not near the 20 GB I used to have. Luckily, the agent was able to restore my previous admin from a Microsoft account to a local account.

What I think I need to know is what folders Windows Update, ESU, and System Restore use. I'm hoping I can go there, find the files changed yesterday afternoon / evening, and see that they take up nearly 20 GB... then I'd delete those files. For example, does ESU signup create C:\Windows\XYZ123? If you have any other suggestions, I'd sure appreciate them!