I did an extensive set of tests (including the cutree option, and many others) and compared until I found the settings I preferred.
This is the line I entered into the 'extra options' in Handbrake:
aq-mode=0:rd=6:rect:amp:cu-lossless:rd-refine:strong-intra-smoothing:rdoq-level=1
sy-rdoq=50:deblock=6:6
(it says ' psy-rdoq=50 ', not a smiley of course)
(Using X265 set to 'medium' and with fast-decode unchecked)
This gave me an image quality at around 2000 kbps that worked for the video I worked with (faces were sharp and walls and doors and floors were blurred a bit)
And then I discovered that the Chrome-browser can not play x265 videos
I should have checked that first, but oh well lesson learned.
So I googled around and found out which video-types the various web-browsers support, and are now focussing on WebM-VP9 instead.
Sometimes video-encoding is just SO much fun...
Anyway, thanks all for taking time to reply to this thread