Cannot save pages after migration

I would first do the same procedure you outlined in your comment with one of the ‘twenty’ themes. If that fails, then I would temporarily disable the plugins 2-3 at a time to see if that makes the problem go away.

Also, just for grins, do a reinstall of WP from the Admin, Update page.

And, I would check the version of PHP on the server, comparing it to the development server. I’d aim for PHP version 7+ if at all possible.

If going to one of the ‘twenty’ themes doesn’t fail, then I’d contact the theme support. Likewise with a plugin that appears to be causing the problem.

Use your test procedure after each change. And backups of the database before you start making changes might be good also.