Hello,
1) Provide us with link to the product where you have the “Uncaught TypeError: Cannot read property ‘classList’ of null”
2) I did not face issues with checkout the https://prnt.sc/10tb00z Describe your actions step by step to get the mentioned issue. Did you try to enable default Storefront theme and test the order? Do you have this issue?
3) I see that third-party plugin generates errors https://prnt.sc/10tb438 So, contact plugin author to fix the problem because it’s not good.
Regards