Hi guys, posting this in the hopes that it helps someone else plagued with the Dx11 crash.
A few months ago I was getting sporadic crashes with FF14, I couldn't figure out what on Earth was causing them, the only improvement I was able to find was using a specific BIOS version which made the crashes less frequent (I could still encounter a crash as soon as I logged in, or after 2 hours+ of playing). I wasn't having issues with any other games and given the numerous other complaints about Dx11 crashes with FF14 I expected it to be a bug with the game.
I tried everything I could think of/what was suggested, reinstalling windows, disabling overlays, compatibility mode, changing drives etc. Then the other day I found a video that suggested running Prime95 to see if any errors were found. I had run other benchmarking tools and had no issues (memtest, cinebench etc.) and at first I had no errors in Prime95, but after letting it run for a while it eventually gave a rounding error on one of the workers (as the video had shown), disabling the core that had the error seemed to fix this, along with the Dx11 errors. Given that my build was running at stock settings it shouldn't be having any issues, but I wanted to try and resolve the dx11 crash without having to disable any cores. I had a look into what could be causing this and saw some suggestions that maybe the CPU wasn't getting enough voltage and that this could cause the rounding errors. I changed the Precision Boost overdrive from Auto to Enhanced Mode 4 in the BIOS and now it appears that the Prime95 rounding error is gone, so is the dx11 crash and I don't need to disable any cores! I have been playing for a few days with no issues so I'm quite hopeful that this was the fix for me. Strange how this issue was only occurring in FF14 though...
I'm using a Ryzen3700x so not sure if these issues can be fixed in a similar way for intel, but hopefully this helps someone else!
TL;DR: PC running at stock settings, months of Dx11 crashes (FF14 being the only game to encounter any issue), ran Prime95, eventually had an error show, changed Precision Boost Overdrive in Advanced CPU config in the BIOS from auto to Enhanced Mode 4 and now all crashes have stopped without having to disable any cores.