This issue is present on Canary 3277, even after a related patch was made (https://github.com/citizenfx/fivem/commit/95cdaf0e7f7b1783817b02cb37780166bcf6b7b1)
A custom keybind created by the RegisterKeyMapping native will cause the client to hang then crash.
Binds created manually using the bind console command do not have this issue.
(a crash dump, in case it’s even remotely useful)
CfxCrashDump_2020_12_07_23_32_40.zip (1.6 MB)
A simple reproduction is to run this snippet on the client, choose a key in the menu (or have a default bind), then click the specified bind.
RegisterKeyMapping("testcmd", "Hello World", "keyboard", "NUMPAD2")
A bunch of people had already mentioned this on the Discord server, but since that usually ends up in thefeed purgatory after 2 minutes I figured a simple bug report would suffice.