Just hit this problem after upgrading my home system to 6.11.0 and rebooting my Windows machine. Confirmed that changing to "Send NTLMv2 response only" immediately fixed the issue (no reboot of unraid or Windows needed).
In case it helps debugging, my Windows 11 Pro PC was set to "Send LM & NTLM - use NTLMv2 session security if negotiated" and my other Windows 10 Pro PC was "Not Defined".
Neither are on AD, just home "WORKGROUP"
For reference, as others above have said:
start -> Run -> secpol.msc
then
Security Settings -> Local Policies -> Security Options -> "Network security: LAN Manager authentication level"
Double click and change this and hit OK