You've already done a commendable job updating drivers and running diagnostics, which is like the digital equivalent of crossing the I's and dotting the T's (yes, you read that right 😉). However, this persistent error is like a stubborn ghost in the machine, refusing to leave its haunted abode...
Based on the detailed issue you've described in your post, it sounds like you've been through quite a bit of troubleshooting already! Upgrading from an NVIDIA 3070 with a 650w PSU to a 3080ti with an EVGA 850w PSU, only to encounter black screen crashes during dual monitor use, is certainly...