Deprecation Errors - How to Fix?
I'm not sure I can tell you much more than the error messages are telling you, you need to update your twig code eg. in index.twig (line 6) where it says; getPurchasableId() change it to getId().

These errors are just warning you that a future version of Craft won't support them (I imagine it will be Craft 4, but could be sooner).

Changing e-commerce systems based on this error would not be advised as it's a very simple fix!