Was having the same issuee, found a solution (sort of). It is a Chrome extension, but seems to work as it should on opera as well.

Sprucemarks
https://chrome.google.com/webstore/detail/sprucemarks/fakeocdnmmmnokabaiflppclocckihoj/related?hl=en

Hope this helps!

@gamadrila Sorry, I forogt to explain it properly; once you have the addon installed, you have to click on the "Sprucemarks" addon that should be in your addons folder and sort from there. It is a bit more tedious, however there doesn't seem to be any better option that I have found...

@Gamadrila I am able to see the options on my version of opera; if you select the add-on and scroll down to "Other Bookmarks" which is esseentially just all of your other folders excepting the bookmarks bar and click on the drop-dwon that probably is shown as "..." or another sorting option there is an option for Dorting by Date > Newest to Oldest or Oldest to Newest. Also don't forget to activate "Automatic Sorting" if it isn't turned on by default (Am not suree if it is or not). Hope this helps, might just be different versions of either the Add-On or Opera itself too...

Was having the same issuee, found a solution (sort of). It is a Chrome extension, but seems to work as it should on opera as well.

Sprucemarks
https://chrome.google.com/webstore/detail/sprucemarks/fakeocdnmmmnokabaiflppclocckihoj/related?hl=en

Hope this helps!