Oddly mobi may have some features not in azw3/KF8 or epub2. It may have supported limited interaction, a database and a directive to block paging to next part, so you could have parts only accessible via links. The documentation was sparse, but I still have a copy of the last Mobipocket book Creator on an XP VM on Linux copied off a laptop bought in 2002 using MS Disk2VHD (some experimenting with settings needed with Disk2VHD and also with Oracle Virtual Box on Linux (Update from Virtual Box 6.0 and earlier to 6.1 disables Direct3D support on XP, but not Win7. Unfortunately nothing I have on XP using Direct3D runs on Win7.)
Mobipocket Creator Publisher Edition 4.2 build 41 still works on XP via Virtual Box 6.1 on Linux Mint 21.1
I used it till I switched to Calibre for ebook creation. Originally with Word 2002, but at the end I was importing pre-cleaned HTML (in Notepad++) exported from Word and then Libre Office.
https://learn.microsoft.com/en-us/sy...loads/disk2vhd
Will "export" a VHD from 64 bit Win7 on a UEFI bios PC, despite claims it can't, but obviously only if the Windows 7 was installed in Legacy Boot mode due to BIOS setting = Both.
Amazon no longer accepts mobi on KDP, but big publishers can do stuff KDP users can not.