After all this time and trying updating windows 11 to latest, troubleshooting, clean install windows and searching the web for a solution I came across a suggestion that deleting - usn journal - may help resolve some ssd / nvme performance issues, and I was completely desperate, so I gave it a shot.
Reference article for the fsutil usn command, which manages the update sequence number (USN) change journal.
learn.microsoft.com
using the command ( fsutil usn deletejournal /d c: ) described in the above page, I deleted the journal, nothing appeared to happen, ran some tests, the file copy speed seemed to got a little worse even than before.
After few days, I needed to copy some files, and to my surprise the copy speed was -normal- and the problem gone.
Continued my tests until today (copied over 80 GB) and the speed was great.
I am not an IT specialist, but after some extra reading I found out that the -usn journal- deleting process can take some time and will continue throughout several reboots in some cases.
So, if anyone is still having this issue, this -maybe- the solution, again I am NOT an IT specialist, I just posted what I tried to solve the issue, please search and ask some experts before resorting to this method.