Thanks for the update.
MSI vs MSIX installers should not matter, as far as I know. I use the MSI version myself. The running application should still be Photo.exe.
Other ideas:
1. Did you change the shortcut for the Copy Flattened command to something other than Ctrl+Shift+C? If yes, exports will not work. If you did not change it, please try a manual test by using the shortcut directly and confirm it will paste correctly into MS Paint or some other image tool.
I will need to add flexibility to BMP Export to support custom shortcuts anyway. That's actually something I had not considered yet.
2. Have you tried different images? Very high res images in particular can sometimes fail export. I'm working on an update to hopefully mitigate this.
3-Are you using a clipboard manager? That might interfere with the export.
Thanks for your patience addressing this. There is an answer somewhere, it is just a matter of identifying the right variable in the situation. If necessary, I'm willing to compile a private debug build of the program for you to test, if that's what it takes to better troubleshoot.