Not too sure on major changes
i know they have different axels on them, meant to be a bit lighter
build quality of the new bikes (including 2020) seems a lot better even down to the nuts and bolts used since KTM took over.
resale value a 2020 is now worth less than a 2021 as its older so the purchase price new will reflect this.
new 2021 looks very pretty in white i must say