We are starting to lack where to mess with… check if Windows Defender is active and disable it. It might be active if there is no antivirus installed. Besides this, I would start changing things to try isolate the responsible in the following order:
- underclock the graphics card
- put another graphics card, can be even AMD (try to use this tool to be sure no other piece of driver is left: https://www.guru3d.com/files-details/display-driver-uninstaller-download.html)
- try other RAM sticks
- underclock the cpu
Experiment with each one at time, don’t try too many mix of changes or it will be hard to tell which one is problematic. Make a list of at least two combinations. Let us know your findings.
PS: On a side note, check if there is no file with a crash dump generated. Fortnite will generate one and a screen will appear letting you to automatically send the report to Epic.