Alright, so I still haven't been able to fix my crashing. It's no longer only in San Myshuno but happens at anytime in any save and it seems to be happening more often all the time. While loading a lot, building, playing, taking pictures etc.
I've tried re-installing the game on my larger E:drive with 476GB of free space (after install) and I have 81GB free space on my windows drive. The game froze after 10 minutes in build mode on the fresh install. I think we can rule out the "not having enough free space on my C:drive"-theory.
I've also monitored my memory use and free disk space while running the game and I can see no peaks in either. At the most the game reduce my free disk space with a 100 MB or so. The game doesn't seem to be particularly taxing on my system. I've discussed the monitoring, memory and disk space with my boyfriend (who has a master degree in computer science) and he doesn't think it has to do with memory or free disk space either.
When searching for a solution I've been reminded of a roll-back from windows 10 to windows 7 I did when windows thought it good to force an upgrade back in 2016. I've read somewhere that the roll-back often messes with a few drivers and doesn't clean up all the files which could possibly be damaging to your system. I'm leaning towards upgrading to windows 10 again and doing a clean install to make sure that my operating system is all good.
I've read in other threads that one might try to create a new user profile and see if the problem persists when running the game from the new profile. I think I'll try that before re-installing windows.
I'm not going to spend §50-60 on a new drive though. I think that advice is a bit harsh especially since I have no problems with any other applications on my computer. I haven't experienced any problems with windows either but it's nice to do a clean install after a few years so I'll do that nevertheless.
I'll try to keep this thread updated with my further testing.