Hi Ed,

I saw Joomla logic mistakes in your question. I want to be sure that you understand what you asked for, if you don't mind.

template that converts articles to articles

None of Joomla Template cannot convert articles, Templates are only to display content, not for migration or conversion. With different templates articles still will be published, they design may be a little bit different, but that's all.

I don't want to rebuild the articles into modules

Nobody does, to be honest. Bad idea, also becuase Modules cannot be a menu items or displayed as blog view. In general, in most cases, Modules are to display content from components, like Articles etc.

Joomla 3.10 > Joomla 4

Template facts / the main answer:

• In most cases using Helix Ultimate (the raw one) will do the job as new theme.
• Upgrading cms is not always an easy process. Many things can go wrong. I know it from expirence. Many parts of the J! 4.x code have been rewritten and many old extensions may not work anymore or even cause serious problems. For example, an old plugin may crash your site (front or even admin area). Old modules can display long list of errors.
• Template built for Joomla 3 will NOT work in Joomla 4/5. And you have to use a new one, or somehow update its code.
• Joomla 4.4 uses Bootstrap 5.3.x, a new template should use it as well.

Read our guide: https://www.joomshaper.com/blog/how-to-update-your-site-to-joomla-4 (there are also a few guides on YouTube).

If something is made/coded by humans, it can be fixed by humans ;)