I've created a web-based mosaic planner that is completely software agnostic. You can use it to generate FITS files of a fake star-field that can be used by any software that can "solve and slew". I hope you find it useful. After planning the mosaic, just click the "Download X" buttons at the bottom to download each frame.
https://mosaic.darkdragons.space/
https://mosaic.darkdragons.space/