I have a brand new apartment. On recommendation of the constructor (new walls contain lots of moisture that needs to go out), it's set a little warmer than I'd usually go: 21C (70F). In my old place I'd put it at 18C (64F).
That said, currently it's 25C inside (77F). This place is insulated like crazy, and we don't have AC (that still isn't common over here, even for new builds). For reference, current temperatures outside are 14C (57F)
In the UK here, have you guys had a cool, wet summer too? And if so have people (not necessarily you as it seems you live in a modern well insulated home) needed to put the heating on? I'm in a flat in a late 1800s building and have put it on a couple of times to take the chill off, my mum's in a 1920s semi detached and has had the heating on most days.
Our weather is nigh-identical to that in south-eastern England. I mean, after all, coast to coast theres only 100km between us. We've had a normal summer. Perhaps "cool" by today's standard, but even on average for the last 30 years it's been a normal summer.
June in fact was exceptionally sunny and dry. July indeed was a nothingburger, mostly rain rain and more rain. August was a mix, some good days some bad. What we didn't have this year was any 35+ temperatures.