Migrating from Studio still can't update all references to local

I tried rebuilding a website using a new child theme on Wordpress Studio (it seems logical to work locally and only upload changes when they're made).

I'm trying to export an XML file from Studio, import that from wp-admin on the live site, and then reconcile the missing images afterwards (which I still haven't solved, as any newly singly uploaded images will have different URLs and it can't see SFTP'd images at all). This seemed to work. Better Search Replace found only two references to localhost, both in posts, so I replaced those.

This doesn't transfer my child theme, and when I do, my website starts trying to access my local computer. I removed one reference to localhost from the theme.json, and nothing in any file on there has a reference to it. I'm not sure what to do at this point.

Every other plugin or upload option fails. Cloudways' own migration plugin can't do Studio. The database editor fails because, while it says it supports the collation, it won't recognize it when I try to upload. Updraft's migration wanted access to the local computer and broke some (not all?) images. Duplicator is looking for a function that I think hasn't existed for years from what I see on Google (mysqli_real_escape_string) and failing me because it requires it. WPvivid gives a blank screen if I try to restore using it. (I haven't tried paid versions of plugins, because at this point I think I may need a Wordpress alternative).

It works locally. Talking to a friend who's been doing this successfully for years, it should be as easy as export, import, let Wordpress sort out the URLs itself, maybe toss in a theme, upload and replace images manually. I'd expect SFTP to solve most of my updating needs anyway. What am I missing?