This post shows how to re-enable Tampermonkey. -> https://forums.opera.com/post/162138
Then please export your scripts (with script storage) and install Tampermonkey BETA from the Chrome Web Store. It is not blacklisted (at the moment).
I already contacted the review team via my Opera extension developer account and they are saying, that they have a reasonable suspicion that Tampermonkey is also distributed by some malware. I'll update the Opera version as soon as possible.
Sorry for any inconvenience.