In an ideal world, I support one of the opposition parties to Hamas.
But pragmatically, in reality, that's just not feasible. Palestine's main defensive power is Hamas. So while I agree it's an Zionist Regime vs. Palestine conflict, Hamas is to Palestine what the IOF is to the Zionist Regime - that is, their military power. It doesn't really mean much if someone "supports Israel in the conflict but doesn't support the IDF", that doesn't make sense outside of abstract ideas.
For what it's worth: something I haven't seen come up (so while this is a pragmatic perspective, don't pretend I'm dismissing the importance of your relationship and your values! I'm only adding this for variety and discussion)
People can change. Many won't, but some do. [vid: former white supremacists describing their process of leaving] Whether you think your brother is willing or able to change is your call, and whether it's worth the emotional and mental strain is your call. You aren't obliged, but it's worth considering.
People who have left these ideologies, from what I've heard, often come back to two main points - they had someone in their life who cared about them, but was also unwilling to tolerate their bullshit, and they had to want to leave it by themselves. Honestly, I see parallels with people recovering from serious drug addictions and cults like QAnon.
But, again, this isn't easy and there's no guarantee of them changing, so do not feel obliged to even try. Your health is more important, and there are plenty of other ways you can help change the world.