I stopped using Opera and switched to Vivaldi and I can assure you it's not Chromium as I have absolutely no "outofmemory" issues using Vivaldi so far (and used it for days now).
I have a 16GB DDR system , Windows 10 , SSD and opera showing outofmemory messages is absurd (btw, if you had a real 64bit version this error would have not appeared:) there is clearly a memory hole in the code introduced with the latest patches/versions. T
Anyway , it is definetely something related to opera last 2 versions (just compare the code and see what you added and do a proper smoke and regression testing this time) , frankly this is a job for QA (if there is something like that at Opera or devs/enduser is the QA?) but i think Developers should look into the code for this and see what sites are causing it , have a debugger running and also checking the process to understand this bug. A end-user cannot do nothing here but experience it.
My Opera configs :
1 Adblock Plus
If we are on the logic that only 10 experienced it and as such it's not important ...well there are other browsers.