windows 10 (October 2018 update) (version 1809) deleted all my files

This is not a general issue. I didn't lose any files when I updated to Windows 10 version 1809 on October 4th nor from any of the updates that have been issued since:

Now I am using an HP Desktop PC 510-p009 64 bit.

I do NOT have OneDrive installed. I don't LIKE OneDrive (as an automatic process, I mean).

Now it would be interesting to learn what those who lost files have in common (e. g. make, model, make of Processor, whether or not they have OneDrive installed) etc.

I can suggest that if the issue involves the Update MOVING all a user's files to OneDrive during the Upgrade (I cannot imagine WHY it would do that but some users have said that that was where they found their missing files) it would matter VERY much how much storage one had available on OneDrive. The storage limit for their Basic Plan (free) is 5GB.

So any files OVER that size would be deleted, one assumes. At any rate, they would not be uploaded and unless the computer had additional instructions from the OneDrive part to leave them where they were they might just get deleted.

Now IF this (or something like this) happened Microsoft would have no copies of your files and any recovery software would do as well as anything they might propose in the future. 

And again, as most of you were no doubt told in your computer classes in school BACK UP YOUR FILES. I know, that doesn't help now but, seriously, there was a reason your teachers brought that up.

This is that reason: "If anything CAN go wrong, it will."

And, finally, install WUSHOWHIDE to help you in avoiding further Updating issues.

For Get Data Back I run it on another system with the drive attached via a dock. We do this on one of our "servers" at the repair shop I work at. There's also a company called Ease US that makes some decent recovery software as well you could try out. Many of their software comes in a bootable format as well.

That is really very bad behaviour for such a update.

Microsoft does not seem to be able to deliver updates bug free. 

Please make feature updates  voluntary!!

They do in their little known LTSB version. Its a version of Windows  without the extra store and cortana junk and only brings security updates instead of "feature updates"

LTSB is a version of Windows 10 Enterprise, not available to the general public.