Cant start VM " Failed to run: forklimits limit=memlock:unlimited:unlimited" LXD 4.0.9 LTS snap

Also just as a side note, the LXD 4.0 LTS series is only receiving security bug fixes now, so for continued general bug fix/environmental change support you need to be running the LXD 5.0 LTS series.

See Managing the LXD snap for more info about the different snap channels.