Game crashing + settings not saving

Right click on ck3.exe , properties, compatibility. Tick "disable fullScreen optimisations" untick every other box in that dialog, Apply and exit.
Then in the launcher Game Settings menu, select fullScreen display mode, Vsync off, cap refresh rate at 60.

Now test with a new campaign when ALL Mods disabled.

If those don't help:
DXDIAG is a program you run from the Windows search box on the task bar. After running it will open a window and start collecting info with a progress bar in the lower-left corner. When it completes click the 'save all information' button and save it to a file then attach that file here.

Please attach here your Documents/Paradox Interactive/CK3/pdx_settings.txt .
From your Documents/Paradox Interactive/CK3/logs/ folder, attach here system.log , error.log , exceptions.log  

You have a memory fault on your machine, very likely hardware I'm afraid!

Memory: 16384MB RAM
Available OS Memory: 8122MB RAM

Half your memory is unavailable in Windows.

Until you can get that fixed:
- expand your Windows paging file maximum size to 32gb

Optional: Increasing the paging file size on Windows computers

On computers that have 8 GB of RAM, the suggested paging file size is 16 GB. www.ibm.com - exit every other app you can before starting the game.

Good luck with that!