Thanks for your question. I believe once a BMP exceeds 4GB most viewers fail. This is because fields in the BMP header are limited to 4 GB, even though the data in the bitmap is unlimited.
One suggestion is to export a TIFF (High Resolution) and use Adobe Photoshop. Photoshop is very good with large TIFF files, but not with large BMP files.
Is there a reason you need BMP instead of TIFF? Can you explain what you wish to do with the large BMP file.
We have a 64-bit Linux version of ACE you can try. Linux will be added to Numerical Cloud fall 2020. Gimp (Linux) works well with large files because Linux optimizes memory better compared to Windows.