Re: Post Magento 2.1.x to 2.2.x or 2.3.x upgrade, product export does not work
Re : I wanted to know if the programming and changelog have had a huge difference that resulted in our themes on version 2.1.x incompatible with 2.2.x or 2.3.x
- We can not say there is huge difference but yes few methods gets deprecated , few introduce with new as well.
so before going to update on production , you need to update on your staging/development server . if all goes well then go with production update.
Re : all the modules and coding structure of 2.1.x is compatible with 2.2.x or 2.3.x ?
- No directly we can not say that all the modules and coding structure of 2.1.x are compatible with magento 2.2.x , if extension developer has used any method which is deprecated in current version then might be that will not working.