The github page says that leavinel's plugin supports writing BPG for xnview only.
See
https://github.com/leavinel/BPG-Plugins
Imagine (Lister plugin for viewing img files) v. 1.9.0 (Apr 12 2025)
Moderators: Hacker, petermad, Stefan2, white
Re: Imagine v. 1.9.0 (Apr 12 2025)
v1.9.0, Apr 12 2025
- Added: Support for DICOM metadata information
- Added: Support for lossless JPEG
- Fixed: Rewritten DICOM decoder
- Fixed: Memory leak when rotating an image
- Fixed: Error loading CMYK color PSD file with 16 bits per channel
- Fixed: Error with TIFF without PHOTOMETRIC tag
- Fixed: Problem with installer overwriting existing ini file
- Added: Support for DICOM metadata information
- Added: Support for lossless JPEG
- Fixed: Rewritten DICOM decoder
- Fixed: Memory leak when rotating an image
- Fixed: Error loading CMYK color PSD file with 16 bits per channel
- Fixed: Error with TIFF without PHOTOMETRIC tag
- Fixed: Problem with installer overwriting existing ini file