Per the release notes, I made use of the upgrade helper which is a plugin you install along with, of course, upgrading your site to Eleventy 3. This worked well and flagged my only issue, using EJS, which is removed from the core of Eleventy and requires a plugin.
If you don't have it last, it won't recognize that you've installed the EJS plugin. Even though it is not required, I thought, why not switch to ESM as well? That was mostly easy as I've found Node to be really quick and clear when you screw this up.
My serverless functions were a mix of CJS and ESM code. I only used ESM in the Netlify functions that used their new 2.X version. I figured, well, assumed, that since the serverless functions don't run in the same context as the rest of the site I didn't have to upgrade them.
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