Hezbollah declared war on Israel, unprovoked, on October 8th through to late 2024, by launching constant missile attacks on civilian areas, notwithstanding their violation of UNSC Resolution 1701. Israel is justified under international law to invade South Lebanon and completely decimate Hezbollah unless it offers an unconditional surrender.

I am more sympathetic to your views regarding Syria, however. That is a less justifiable war with nebulous preventive/preemptive motivations, which is somewhat coherent on a pure self-interested security basis but is likely validly unjust under different frames of reference (morality, modern global norms and taboos, and international law).