There are applications that won't run properly on Windows 11. I haven't tried the GroupWise 2014 R2 client.

Did you try running the GroupWise client in compatibility mode?

Can confirm this. Likely it's time to upgrade.

I didn't think to try manually setting a compatibility mode, as I can count the number of times compatibility mode has actually made a program work on the fingers of an old shop teacher's hand and still have a finger or two left over...

but you're right, couldn't hurt to try. I have an 11 24H2 test system on my desk at my regular job, I can install 2014 R2 SP3 and try it after hours

GW 2014 still uses and needs MAPI underneath, and it seems Microsoft has now finally blocked/broken it in W11 24H2. Groupwise isn't the only affected:

https://learn.microsoft.com/en-us/windows/release-health/status-windows-11-24h2

I wouldn't expect Microsoft to ever fix this. The solution in googles case is to update google workspace.

In these cases I love to use ZAV (Zenworks Application Virtualization) alias Desktop containers alias Hybrid Workspaces 

I have this issue as well. Since I have a support agreement with them, I open a case with them.  They that do not support 14.2.3 anymore and to upgrade it. SO calling them will not help you.  I think that since there are 2008 C++ stuff in it .. it won't properly initalize..

I have had everyone thsi working with windows 11 decline the upggrade to 24h2..well either this or turn on imap and run the PCs with outlook for every thing new. I have no Idea what to do about archives.

I had to rebuld a laptop that 24h2 with 23h2.. because the person wanted to use the client and not the webaccess or the Outlook..

No fixes just horror stories.

 I have and it doesn't work 

So what is the best way to go to 14.2.3 to 18..then from 18 to 24??

I am running my GW server on Windows 2012 server.

It has nothing to do with 2008 C++, it is MAPI, like I said.
May I ask what is stopping you from upgrading to a Groupwise version that isn't out of support for over 6 years?