Thank you for reaching out to the community forums for help with your store's online checkout experience. I understand you are having an issue with the cart > checkout flow. I was able to replicate this issue on my end as well.
While I can't say for sure what caused this issue, I am able to see that there are multiple 404 errors on the cart updater when activating the checkout button:
Are you trying to navigate to a third party checkout experience, or are you using an app that has it's own checkout? If so, you will need to contact the app developers for that app for additional help. I would recommend in this situation to create a backup of your theme file (Online Store > Themes > Actions > Duplicate) and roll back the theme code for the cart to it's original version. If you have any apps that edit or customize the cart page, you may need to reinstall them to get them to work once again.
Generally this is an issue with the theme file itself and you can test that by loading a fresh copy of the theme on your store and seeing if you are able to load the checkout. If you are, then you know that something changed the code for your cart and that is affecting your checkout loading.
I hope this information helps you isolate and resolve the issue!