Disc Utility First Aid on iMac HD error msgs.

From what I can find, it has to do with the new APFS file system which was just implemented with Catalina. However, since all your volumes were checked and the end result is "successful", I wouldn't pay any further attention to it.

I am not a Disk Utility expert, but I always look at the bottom line when the report is completed and it usually says the disk is ok, sometimes after fixing something. It is a good idea to rerun the DiskUtility app until you get a final ok report as sometimes it keeps finding things to fix, or seems to ignore some.

If your computer is working as it should, I personally wouldn't worry. As noted elsewhere, EtreCheckPro is a free download app which tells us the status of our os. It's not too hard to understand and is very useful. It does show orphaned files, etc. which it recommends removing. However, I should mention that it does also show some files which are hidden and are not visible. I don't worry about them. Try it and see what it says.

With the information you have provided, your question can not be answered. You do not show what the result of the Disk utility scan was. What prompted you do do the scan in the first place? Did you have a problem? If so, what? also, it is very helpful to tell us what model and year of Mac you have as well as what os it is running. If your problem can not be resolved, there are additional steps which can be recommended.

That's what I was thinking, but wasn't sure. :)