rootkit after updating to version 2004(windows 10)

Viruses and worms
1

I updated to version 2004(i had the 1903)and i did a full scan and avast found files(which i cant find when i go to the location avast shows me they are,they are in the file ‘‘windows.old’’) infected with rootkit.Just a day before the update i did a full scan and it found nothing.(except a ghost with a red icon but i saw that was
nothing serious.)
I click to delete these files,then i do a full scan and again the same .i delete them again and do another full scan.The same continues to happen…

2
''windows.old'

Delete your previous version of Windows
https://support.microsoft.com/en-us/help/4028075/windows-delete-your-previous-version-of-windows

https://www.google.com/search?rlz=1C1GGRV_enFR784FR784&ei=gjJaX6qJL8n9kwWTjb2gBw&q=how+to+delete+windows+old+in+win10&oq=how+to+delete+windows+old+in+win10&gs_lcp=CgZwc3ktYWIQAzIECAAQHjoECAAQRzoGCAAQBxAeOggIABAIEA0QHlC55AJY0P8CYNHsBmgAcAJ4AIAB3QGIAcILkgEGMS4xMS4xmAEAoAEBqgEHZ3dzLXdpesABAQ&sclient=psy-ab&ved=0ahUKEwiq0u_p4N7rAhXJ_qQKHZNGD3QQ4dUDCA0&uact=5

3

any explanation why this is happening?

4
any explanation why this is happening?
False Positive
5

If you have just updated to new version of Win 10 then you may wish to keep the old version for a few days until you are sure 20.04 is working properly and you feel you have no need to roll-back. Also assuming the two ghost reports are just false positives mentioned by Pondus.