Workarounds for the guaranteed crash when attempting to start Arena Mode that many of us have experienced when attempting to obtain the Grandmaster achievement.
Guide to Crash Workaround
Why Does It Crash?
The problem seems to be related to multi-threading when loading data. The more CPU cores you have, the more threads the game uses, and for some reason attempting to start an Arena Mode match just completely breaks, with a guaranteed crash on affected systems. From the reports I’ve gathered, an 8-core or higher CPU is a guaranteed crash, and a 6-core CPU may crash as well.
Don’t waste your time trying to fix it by adjusting graphics settings, those don’t matter at all.
If you have access to an older/weaker PC with 4 or fewer cores that can run the game, use it to enter Arena Mode. If you have a Steam Deck or another brand of handheld gaming PC, those will do the trick.
For those people who don’t have access to another PC, there is another workaround: disable all but 4 CPU cores temporarily. If you have an AMD Ryzen CPU (excluding the 5800x3d,) this can be done with Ryzen Master. You need to disable some cores, restart, get your achievement, then go back to Ryzen Master, hit the Reset button and restart again to bring the CPU cores back online. You should also be able to disable CPU cores in your BIOS, or use Windows’ advanced boot options through the msconfig utility as shown here (again make sure you reset this when you’re done):
I hope this helps some more people.