That's the list of breaking changes we've made in the past 10 years since v2.6, but it might very well be you won't run into them, or only in some cases. For every project it's different what the impact will be, so all we can do is give a list of 'this has chanced', sadly. I'd at least look through it from bottom to top, where most changes are around v2.6->v3 and v3->v4. From v4->v5 is rather uneventful and shouldn't affect you much.
Additionally, many people before you have migrated away from v2.6 to v3 or higher, and it's likely if you run into an issue regarding migration it's already been asked here so you should be helped with these answers pretty quickly (unless your issue is unique of course ).