I hope asking a question about Wikipedia is not against the rules, couldn’t find nor confirmation nor contrary in the sidebar.
I have a PocketBook reader that doesn’t support Kiwix. Would need an EPub or another primitive text format. I know a tool to save an archive on epub exists, but no already packed thing with a top 50000/100000 collection.
There is a plugin for calibre ebook software which can generate an epub file from selected wiki articles. Last time I looked it worked fine.
If you can run Python code off GitHub on a computer, I’ve never used it, but this tool on GitHub purports to do that. Hasn’t had any commits in the past three years:
https://github.com/jonbirge/briki
This one apparently lets one convert one or more WP articles to a .epub, and is getting commits:
This one updated 10 months ago
I don’t know of any epub format sources, but it is possible to set up a static copy of Wikipedia on a personal computer using Wiki Data Dumps and Kiwix. Mayhaps that could be a starting point for public access or conversion.
Not exactly what you asked for, but koreader can download and display Wikipedia articles on demand (on a long press of a word). A quick google search seems to indicate koreader supports some pocketbook reader.
For books, a manual method is to choose a book with the Wikisource Reader app
https://f-droid.org/packages/org.cis_india.wsreader/
Press Download button, and then view them in the Wikisource library tab, click the share-icon, and choose the Save Locally app
https://f-droid.org/packages/com.mateusrodcosta.apps.share2storage/
