Hi @doughballs,
Do you mean the About is the existing page before the builder or WPML is installed? Old or new, you would still need to create translations for them. I checked the About and it still has no translation, and you can confirm that since there is a + icon and there is a text “Add translation to French” when hovered.

This is the reason why there is no About page when you switch to French (Question #1, (see about1 and about2)). Hence it’s not an issue, it’s just that there is no translations for old or newly added page. They did not disappear, you haven’t yet provided a translation so there is nothing to list on French listing.
You can click the + icon and it will create a page as a translation of your About page. Then you can just edit the created page within the builder. That’s another way of translating it other than creating it within the builder. But that means it will always start empty within the builder.
By the way, request for translation in WPML! will not work, you’ll have to create your own translation since the content is coming from the builder.
And yes, you could choose French once you’re within the builder then instead of starting from blank, you could start with the existing page (Copy Existing) which will give you same set of fields or contents, then you can just ammend the content for translation. That’s actually how it should be translated instead of clicking the + icon.
Then about the error from the builder, there is an internal server error. I’m trying to disable the WP Rocket plugin but it just activates back. Could you try disabling all other plugins not related to this issue? Then let’s check the builder again, this error is not related to WPML nor the builder but they get affected.
Thanks!