Which version has the least number of changes compared to hugo version v0.96.0?
I’d recommend you either stick to your current version or correct the errors on your site/theme causing compatibility issues.
Or if you’re still determined to do it your way, then dig through Hugo releases.
By definition, that would be… v0.97.0.
Its my first time working with hugo so if I am updating to v0.100.0, what could be the key changes that I have to look for other than themes or plugin updates?
As @Arif said above—the only way to know beforehand is by reading the release notes. There’s lots of information in them, but you mainly need to look at the ‘what’s changed’ section.
Depending on how complicated your theme is, I’ve found it’s fairly easy to upgrade hugo and see what error messages it gives. There aren’t breaking changes very often, and those that happen aren’t all that hard to fix.
Any documentations on the error messages types and their corresponding fix?