Me, again. Not tech this time.

[TommyT139]

1. Keep this link handy

For an alternative program, would Libre Office work for your purposes?
https://www.libreoffice.org/

In the event you want to convert files you previously worked with, before you figure out a whole new program suite, this site is worth checking out:
https://www.freeconvert.com/pub-converter

I have used Freeconvert for converting hundreds of files, from one audio format to another, epubs to pdfs, mobis to epubs, across graphics formats, etc. It handles quite large files, and deletes uploaded files after eight hours, so download the conversions before then. (To be safe, I don't use the site for documents containing personal info.) I have found the quality to be excellent. Sometimes I use up my free conversions per day, but I just save things for next day. I haven't used Publisher for a long time, so check the output against your original file.

There are others in your situation, so boards like the MS support forums could be useful too.
https://learn.microsoft.com/en-us/answers/questions/5724939/how-to-convert-existing-publisher-documents-to-edi

Good luck!

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Update: Further down that Microsoft support thread, there is a link to a tutorial on working with Publisher files using the Libre Office suite. So my instinct seems to have been correct. And Libre Office is free - no more money to the oligarchs.
https://shunspirit.com/article/how-to-use-purblisher-files-in-libre-suite-of-programs