I use Dual Monitor tools to control mouse pointer . event viewer has a lot of yellow and red issues but all refer to dcom , kernel, disk and so. Three monitor of different sizes and 46'' tv connected

Had this same issue. Running the purge_start11 script fixed that particular issue for me.

https://forums.stardock.com/486022/start10-support-faq#reinstalling

And so, the fun stuff. I ran the Purge_StartALL.cmd which generated several errors, as seen in the photo taken (no print screen or copy to paste option due to how it ran). I removed existing setting as I do. After a re-boot of the PC, I re-installed Start11 v0.9.

Single taskbar = no issue. But the moment I turned on "Show my taskbar on all displays" I got the explorer running higher CPU, slowing the machine down, with the "hourglass" when I moved the mouse over the task bar. Once I was able to turn off "Show my taskbar on all displays". The taskbar ran as normal, with no hourglass.

Below is a screengrab highlighting where the option is turned on/off within Win11 and the Start11 app

The photo of the display having ran Purge_StartALL.cmd as downloaded from your link.

SHA-1 0B404C725446BDABA027CF5A99A18AA49C6A66E8

Interesting the script references Start 8 (which I have used, when it was THE app). The script appears to have done the work I already tried.

Removing existing settings

The copy of Start11 v0.9 used from your website, has a hash of SHA-1 3BAFA2BADF3ABA4E360EC2C8427C4870B366561A

As noted, I removed curtains. As for Groupy and Fences, both apps are running as per within windows 10, meaning no issues. Both are used as they do serve (for me) the purpose they are designed to do.  Are you really saying un-install don't use your apps on win11?

For clarity I have run windows 11 moving from Dev and Beta channels. All Stardock apps installed have worked without issue. * Curtains was not installed on the 3 screen PC, only the single screen PC.

Again, the first two beta's of Start11 worked without issue, on the 3 screen PC. The only change on the system is V0.9. If I clean out all Start11 data and re-install an early beta it works, as intended. 

Same issue here - Blank Taskbar / Crashing Explorer / Heavy CPU Utilisation

Triple monitor setup - left/right/center config - Scale at 100% - Start Menu aligned left.

I initially updated from the 0.5(?) beta - Then uninstall/re-install - Then uninstall with remove settings/re-install - Now Purge script/re-install.  Reboot between uninstall/re-install and also directly after install.  Same crash each time.

In place upgrade to retail Win 11 Pro 21H2 (22000.194) - Beta worked without issue - 0.9 has forced me to uninstall completely to be able to work.  I don't have any other Stardock products or any monitor management products that could have an impact.  As I said, on the beta, it was 100% fine.

Application log just shows unknown errors causing explorer.exe to crash and System log shows Start11 terminated unexpectedly, but no other info.

I did find a bunch of errors in the system log though:

Error 08/10/2021 07:27:40 Microsoft-Windows-DistributedCOM 10010 None The server MicrosoftWindows.Client.CBS_1000.22000.194.0_x64__cw5n1h2txyewy!CortanaUI did not register with DCOM within the required timeout.

Error 08/10/2021 07:27:39 Microsoft-Windows-DistributedCOM 10010 None The server MicrosoftWindows.Client.CBS_1000.22000.194.0_x64__cw5n1h2txyewy!Global.IrisService.AppXk4vtemtqrygqybv239mnaysgpbnbzdjr.mca did not register with DCOM within the required timeout.

Error 08/10/2021 07:27:39 Microsoft-Windows-DistributedCOM 10010 None The server MicrosoftWindows.Client.CBS_1000.22000.194.0_x64__cw5n1h2txyewy!Global.Accounts.AppXrjkczk9sedea5x6ev4segkbdds1ceg32.mca did not register with DCOM within the required timeout.

Error 08/10/2021 07:27:38 Microsoft-Windows-DistributedCOM 10010 None The server {AB8902B4-09CA-4BB6-B78D-A8F59079A8D5} did not register with DCOM within the required timeout.

Error 08/10/2021 07:27:36 Microsoft-Windows-DistributedCOM 10010 None The server Microsoft.Windows.StartMenuExperienceHost_10.0.22000.37_neutral_neutral_cw5n1h2txyewy!App did not register with DCOM within the required timeout.

Error 08/10/2021 07:27:36 Microsoft-Windows-DistributedCOM 10010 None The server MicrosoftWindows.Client.CBS_1000.22000.194.0_x64__cw5n1h2txyewy!CortanaUI did not register with DCOM within the required timeout.

Error 08/10/2021 07:27:35 Microsoft-Windows-DistributedCOM 10010 None The server {9BA05972-F6A8-11CF-A442-00A0C90A8F39} did not register with DCOM within the required timeout.

Error 08/10/2021 07:21:34 Service Control Manager 7031 None The Stardock Start11 service terminated unexpectedly. It has done this 1 time(s). The following corrective action will be taken in 2000 milliseconds: Restart the service.

And if so, and you do not have a custom image, does that resolve the issue?

Sean Drohan
Stardock Support Manager

I had the issue and both of the above are true. Turning the "Use Custom Start Button" to off and rebooting resolved the issue for me.

Interesting comment. So now, I have all four of my installs installed.

And back to the problematic high CPU usage and the taskbar issue with multi-screen setups.  Firstly, I have the start button and menu to the left position of screen.  Now the custom start button option. It's ON by default!!! Otherwise, how would you tempt users to use your/ or their own custom start images. I personally have only used your stock options (going back to Start8).

Now having turned OFF the "use a custom start button image" within the app. Then I then turned ON the multi-screen taskbar option in windows settings and behold all three screens now have a taskbar. Since you have offered this option and it works. I can only guess you have found a coding issue relating the "custom start button" that creates the issue (high CPU and taskbar not functioning appropriately) for so many people, with more than one screen.  

This means until you resolve the coding issue. It would be wise to let users know that you should turn OFF the "use a custom start button image" within the app". Until you have a working solution. Below is the option what users with multi screens should set to OFF. Now the taskbar is using the Windows11 default image.

Is that on all monitors and is it just Start11config that needs to be open or any window at all?

for me  setting the taskbar to only one monitor solves all issues

except:

widges panel  big and strange

windosw 11 widgets

widges panel  big and strange only in primary monitor

I had honestly thought I tested this, but apparently I didn't.  If I have any window open on my main monitor it works fine, the moment everything on that screen is minimised, it reverts to the Windows start menu.