Basically on Hard Mode the Wither is impossible to kill on single player unless you have a bunch of totems of undying which I find kinda stupid because it means it's WAY too hard. Even with full blast prot, you can't even get near him without using at least 2 totems of undying (which can be pretty rare unless you build a raid farm).
Can confirm the bug is still in 1.19 prerelease3