Upgrading to this version caused Opera's memory management bug again. This bug makes the tab threads take up ~50% more memory. There may be an increase in the main threads (esp browser & GPU) too.
What's different is that eventually ie after 30 mins, the memory management has worked and everything looks relatively normal again. It would presumably take less than 30 mins if the system wasn't swapping like crazy.
Having used Opera for around 30 years now, I'm very sensitive to such large changes in memory usage. I have little doubt that overwriting the installation with the previous version will fix the problem but I'll hold off for 24 hours in case someone wants to investigate it. I know from previous threads that I'm not the only one with this problem.