@leocg yes. I tried to opt for "sign in". But it treated like a new registry. It did not recognize my registered account e-mail

@leocg yes, I'm pretty sure. I also have it written in a physical notebook which I already double checked.

After I re-setup my PC, I tried to login to my Opera account to sync my previous stuff, l,ke I did several times in the past. But this time, the page treated me like I haven't had any history with Opera and re-created a fresh account instead.
Now I have a fresh account which is registered with the same email as before but nothing to sync.
I'm a long time fan of Opera browser(s) and I appreciate everything you did so far. Even if this issue does not get resolved I will probably still keep using Opera but with a bitter memory. It is not only web history or bookmarks which have been accumulated over years, but I was heavily reliant on your password manager feature. Now I have to figure out a way to recover some of those passwords the hard way..