We want to test using the store with onepage checkout not enabled. But after turning off onepage checkout, the cart no longer has a checkout button. You can put items in the cart, but there doesn't seem to be a way to get to the checkout page. Did I miss something?
Magento default settings
Admin >> Store >> Configuration >> Sales >> Checkout >> Checkout Options >> Enable Onepage Checkout >> Yes.
This options by default enabled, it is showing 2 steps checkout with one page, not one step.
If you need to one step checkout, you need to install 3rd party extension for one step checkout. You disabled Magento checkout page so it is not showing Proceed to Checkout.
Note: One step and one page both are different, Magento give only one-page checkout not one step.
Ok, I think basically the key part of what you're saying is "you disabled Magento checkout page so it is not showing Proceed to Checkout." So if we turn off onepage checkout, checkout no longer works because Magento doesn't have an alternative option installed (I assumed it would use a multi-page checkout process, but that doesn't seem to be something that exists without a plugin).