The latest version of Opera Mobile Classic available on ftp.opera.com and get.opera.com is 12.1.6. Where can I download 12.1.8 apk file beyond Play Store, for archival purpose?

Sorry for my fault for not noticing the opera:flags option, but the Link feature currently provided does not include bookmarks, which is my most used portion inside Opera Link. Only able to access my bookmarks through link.opera.com is not an option to me.

Opera Link just isn't implemented in the newest stable version yet.
Yes, not yet. There has been ONE year since Opera's initial transition announcement, but to date Link support is still not provided in these Opera 15+ version bumps. I don't know when will they ship Opera with link support; maybe Opera 22, maybe Opera 42, or maybe never?

While not relating with this forum, Opera for Linux is in a similar situation; no definite words of "drop support" or "(supposed) release schedule" is given. Maybe the dev team shall be more clear on this.

I'm curious if there is official way to control Opera's auto update mechanism, just like the Chrome browser do with enterprise MSI installations?
https://support.google.com/a/answer/3204698