What fallacy

“I don't support what the government in Israel has done to the Palestinians, but support for Hamas and what they did is disgusting.”

What is the fallacy, if any?

This would be more of an opinion than an argument, but the opinion is not logically inconsistent. It's a pretty classic example of "two wrongs don't make a right."

If your boss lied on your performance review to keep you from getting a raise, and you responded by peeing in his coffee, a reasonable onlooker would say you both did bad things.

This statement doesn't contain a clear fallacy. It's not absurd like the time I tried to convince my cat to take a bath because "all fur-bearers love water," and he shot back, "What about the honey-badger, genius?" Best I could do was reply, "Invalid analogy, kitty. Just get in the tub." But this Israel-Hamas comparison? That's someone expressing nuanced views on a complex situation, not committing a logical faux pas. So, no fallacy fouls or cognitive bloopers here!

It seems more like expressed opinions than an argument.

However, lingering in the back could be a false dichotomy that assumes disagreeing with one side means one has to agree with the other.