Big parties are big because the majority of the population decided to make them big, if people decide to all vote for a small party then the small parry will be the big party.

That's true (Although most of these big parties were already "the big parties" when me, my parents AND my grandparents were born so it's debatable if "the people" really decided to "make them big"), but if you make a political party that actually calls the genocide what it is and takes a principled stance on israel then you will be cancelled and targeted by an enormous media propaganda apparatus as well as the state and its law enforcement agencies. We can already see people being arrested, sanctioned, fired from their jobs and intimidated by law enforcement for simply attending the wrong protests, voicing the wrong opinions (both online and irl) or reporting on the genocide in the wrong way. There is no reason to expect this reaction to be any milder if you were to create a political party that gains momentum. Similarly to founding a party that actually genuinely demands a different mode of production (i. e. socialism). And with all this we're not even at the point where that party is anywhere near being in government and actually having to manage this nation-state according to the myriad of systems and rules engrained in it to ensure the status quo is being kept up regardless of the personell holding office in it.

This kind of defeats your point about voting in my opinion. I am not trying to justify the governments support of israel, nor am I trying to "excuse" individuals who vote for these parties. I'm trying to tell you that solving these issues requires a critique of the system itself because there are some issues, like gaza or for example capitalism itself, which are simply not up for debate in this liberal democracy. Which brings me to the next thing you wrote:

Many population put their body in the front to stop and overthrow authoritarian regime , you have zero excuse to not try to change the system.

This is a wildly different approach compared to the discussion we've had here about voting for some political party in the elections. I don't disagree with you on this

Edit: If you're interested in a more detailled (and better articulated) critique of this democratic process and its limitations I can wholeheartedly recommend Peter Decker's book/essay collection "Demokratie: Die perfekte Form bürgerlicher Herrschaft". If you don't want to read 200 pages off a stranger's recommendation this lecture about the book is also very informative.