I'm using Wordperfect X7, and it is ten years old, but far from dead.
Link:
https://www.wordperfect.com/en/
I've been using WP since DOS days and will keep using it as long as it is supported, and then some.
By the way, the PC I use for writing runs Win XP, version 2002. For my writing, there is no reason to upgrade. I have other computers for video production, web creation, etc.
The latest versions of WP do export to ePUB. I might try that.
The version I exported from WP to HTML recently looks okay. It even has the right type of table of contents, keeps my fonts, and the photos and illustrations came through, even with the captions intact. It's probably not eBook-ready, but it looks closer than what I got converting from PDF using Calibra. It'll be interesting to see what Calibra can do with the HTML version.