This evening, Picasa suddenly started freezing on Windows 10 here. (Yes, it has been officially discontinued for years now... but for my workflow, it is still much better than many of the alternatives I've tried, and so, until I manage to get my own self-built alternative up and running, I'm continuing to use it...)
After a whole bunch of sleuthing (including deleting my old DB and rebuilding it, in case of some database corruption there), it turns out that the culprit was Windows Defender!
TLDR: To fix this, add an exclusion for the following setting (i.e. "Block Untrusted Fonts") for Picasa3.exe
EDIT: Posted too soon! While doing that gets things moving a little at least, a few seconds later, after letting you scroll, it will again lock up, while it now starts another batch of CPU activity. Doh! (Trying again with disabling a whole lot more to see what sticks...)
EDIT 2: Tried a bunch more stuff, but annoyingly each "fix" only seems to last about 5 seconds before Windows Defender catches on and locks down even harder!
Things that didn't go down well:
* Going through disabling *every* checkbox in that infernal program-settings-override dialog. Doing that just makes it worse it seems!
* Switching "Compatability Mode" to "Windows 8" - This worked for about 5 seconds (i.e. longer than when just doing "open + scroll" tests, but still it locked right up!
Ultimately, after an hour of testing this crap, I'm going have to call it a night on this here, and have ended up filing a bugreport with MS about this... hopefully they do resolve it! Gah!
(PS: The project to again try to migrate my personal workstation to Linux ahead of October just got another massive boost again tonight!)