The last patch doesn't allow mouse look since I messed with the new aim assist. I can no longer play

I’ve raised this for investigation, but in the mean time you may be able to “unbreak” it by wiping your AppData. This will clear any custom options including your keybindings:

1. Press the Windows key + R
2. Enter %appdata% within the search input and select ‘OK’
3. Navigate to AppData\Roaming\Fatshark
4. Delete the entire Darktide directory

If this doesn’t work, see whether Steam Cloud Save is interfering by auto-restoring it. This option is accessible by right-clicking Darktide in your Steam library, selecting ‘Properties…’ and see the ‘Steam Cloud’ option within the ‘General’ tab.