When you get a partially-rendered, unstyled page like this in Magento, it usually means some business logic crashed. The most likely cause is a faulty customization, whether in your own app/code/{Namespace}
directory or in a third-party module or theme.
You've got a couple of options.
If you're using an IDE with Xdebug, you can set a breakpoint in \Magento\Sales\Controller\Adminhtml\Order\Create\Index
. For example, you could set a breakpoint on $this->_initSession()
and step through until you find where the code breaks.
If you don't have access to debugging tools, you can try disabling custom themes, or custom modules that might modify Magento's sales operations. This is a tedious process, but is likely to lead (eventually) to the problem code.
In either case, assuming this is not a brand-new installation and that creating an order has worked up until now, save yourself some time by starting your bug hunt with recent installations or changes.
I wish I had a magic bullet for you, but there's nothing for it but some good old-fashioned detective work. Good luck!
UPDATE [9/27/22]
Based on your response to Luke, it does indeed sound like you have bad code somewhere. That error message ("Uncaught ReferenceError: require is not defined") makes me think RequireJS is not implemented correctly on this page. Meetanshi gives an example of what a RequireJS implementation should look like.
I still think your best bet will be continue disabling third-party or custom modules/themes until you find the one that's breaking. Alternatively, you could look specifically for phtml files (probably) that are attempting to use RequireJS wrongly.