error messages in MS Outlook when he tries to open new emails inconsistently

we cannot render a new actionable message right now. please close an existing one in Microsoft outlook and retry.

Tried all the below possiblilities,

1. Repair the .ost file using tool (SCANPST.EXE)
2. Rename the ost. file and close the outlook and reopen to create automatically a new one.
3. Install a debugger for outlook. This one was recommended for a Microsoft customer support in a forum
https://appsource.microsoft.com/en-us/product/office/wa104381686?tab=overview
4. Also Closed the application and start it back in safe mode, close it again and reopen in normal mode.