you messed too much. bring back backup.
To switch start stop default setting you change only:
Multican-566 MHLastUserMode

That is what I set but so far it doesn't work on my MY21.5 D350.

Mine's 2 centre displays and a fault that affected AEB, Forward alert, CC, CVDs and ARBs had a hissy fit the day before I made the first CCF change. Whilst the displays eventually returned to fully working, the other systems didn't for which I did on-the-fly engine restarts at up to 80 kph with my van in tow to regain those systems for up to about 15 minutes at a time because driving with CVDs not softened and ARBs locked isn't at all comfortable. The display configuration DTCs could be related to this event. L405 D350 SE Carpathian Grey D5 19" rims

try to set ccf "as built" - you can do that with topix or ask gap to give that file*
With mess in ccf you can expecy everything with car.
Then start troubleshooting.

*mine "as built" file on JLR server was wrong, so make backup of actual settings.

If last user mode hasn't started working in a couple of weeks and the fault that occurred prior to any CCF changes doesn't re-occur or does re-occur but doesn't have any connection with stop-start disabling then I'll reset that setting to see if the configuration errors then don't return.

The MY21.5 with the Ingenium 48V mild hybrid engine that restarts using the special starter/generator presumably doesn't use exactly the same stop-start software to what was used with the 4.4 SDV8. Therefore just because something works with the SDV8 doesn't mean that LR has implemented the same capability for the Ingenium engine. Not being a selectable feature, there is no option to report to LR that last user mode doesn't work and being the last of the model run, any L460 updates won't apply to the L405.

I wouldn't have an issue with pressing the disable button every start-up if it was available, but the screen always takes far too long to start, sometimes even requiring the engine to be switched off and a door opened to power-off the displays. L405 D350 SE Carpathian Grey D5 19" rims

if you have wrong configuration. i.e. IMC looks for not existing modules, or could not get correct answer from existing ones then it will restart or initialise again so why you can get unusal long starting of unit.

The only parameter that could be wrong by my changes is the start-stop last user mode being enabled if the software doesn't allow the setting. However this one from the IMC
B1DE3-31 - Multimedia Link - Driver Assistance Domain Controller - no signal (2B)
which was amongst the multitude of other DTCs stored after my many engine restarts on the fly makes me wonder, but possibly the IMC always checks for the existence of a DADC.

I have more options as the engine bay fuse panel has 2 fuses for start-stop if I don't want to disable the 48V system by removing its battery monitoring fuse.

I've been told that the long start-up times for the displays is normal.

Correction: I had made 4 CCF changes 3 days prior to the multitude of faults occurring - disabled 3-flash blinkers, disabled drip wipe, set steering column lock to not fitted and disabled hazards flash on arm/disarm and all changes are implemented. L405 D350 SE Carpathian Grey D5 19" rims

if it starts in 30 seconds then is normal. If starts, then after few seconds restarts again or starts over minute then it is not normal.
You could try reinstall imc software via topix.
Start stop in HEV vehicles is different story, i dont think it is good idea to disable it.
I disablet it that way in my p525 but it is oldscool dinosaur juice powered baby seal killer not eco- shmecko bullpoop.
D350 has more in common with l460 than with earlier l405s.

The displays don't restart and most of the time 30 seconds sounds about right, but sometimes can take a lot longer. If I was parked then I'm gone in under 5 seconds. L405 D350 SE Carpathian Grey D5 19" rims