@leocg No, you can't. And even if you hack into the preferences database and re-enable it, Opera disables it again later. This wouldn't be as much of a problem if there was an obvious way to override this stupid feature.

Update: I seem to have found a way to re-enable blacklisted extensions, though I'd guess that eventually it'll automatically get disabled again and I'll have to repeat the process.

Close Opera and go to your user folder (On windows: "C:\Users[username]\AppData\Roaming"), then Opera Software, Opera Stable, and open "Preferences" in a text editor that has a find feature. Look for your extension's ID (for Tampermonkey, it's "dhdgffkkebhmkfjojejmpbldmpobfkfo"), and look for the entries ("blacklist":true,"blacklist_state":1) next to it. Change "true" to "false", and "1" to "0". Save the file and launch Opera - the extension should be enabled now.

Opera decided to block Tampermonkey for no apparent reason and doesn't give me any obvious way to re-enable it. The scripts are pretty important to my browsing experience... how do I re-enable Tampermonkey? And is there a way to disable this stupid feature that blocks extension without the user's consent?

When I installed Opera and discovered My Flow, I expected this to be an essential feature - but here I am.
I think that being able to send images would be extremely useful - My Flow is intended to keep short bits of information in an easily accessible place while working in the browser; such information is often not just text, but also pictures. It would be very useful to keep them there, whether as a secondary "clipboard", as a way to transfer them to a phone, to use as references for something, and probably a lot more.