Thank you for the report, I have merged a fix. It has been broken since 5.6.4.
KCC had a ComicInfo.xml list index out of range issue when files were chunked. I fixed this issue by disabling ComicInfo.xml bookmarks when no split occured, but I actually disabled bookmarks entirely. Whoops. Fixed now.
Also changed the mobi header from EBOK to PDOC for these devices:
ProfilesKindlePDOC = {
'KO': ("Kindle Oasis 2/3/Paperwhite 12/Colorsoft 12", (1264, 1680), Palette16, 1.8),
'K11': ("Kindle 11", (1072, 1448), Palette16, 1.8),
'KPW5': ("Kindle Paperwhite 5/Signature Edition", (1236, 1648), Palette16, 1.8),
'KS': ("Kindle Scribe", (1860, 2480), Palette16, 1.8),
}
This makes cover upload on MTP kindles way easier and is the only way to get covers on colorsoft. No need to copy a thumbnail file anymore. Or leaving kindle plugged in during conversion.
These devices all can run the earliest kindle firmware that you mentioned that read PDOC covers directly from file.
Let me know if this change might cause issues.
Test build with fixes here:
https://github.com/ciromattia/kcc/pull/767