Bringing the war in Ukraine as a way to measure the relevancy of the use of B61 does not make any sense.
Unless some unforeseen development occurs, Russia only had the early days of the war to use any sort of nuclear weapons in a "justified" way. And I am using "justified" as in: going after targets hardened enough to require that kind of weapon to be dealt with.
As we have seen, the use of high-yield precision weapons were more than enough to deal with whatever Russia had to deal with: ammunition depots. Underground facilities on the other hand were simply besieged and hammered until whoever was left inside surrendered.
With the recent deployment of high yields FAB3000 with gliding kit, using a gravity bomb (let's take a RN28 for the sake of example) would be pointless and merely used to "make a statement".
The war between Israel and Hamas is entirely different in every aspects.
Nevertheless, the use of B61s or any low yield nuclear weapon is uncalled for. Wether it is to go after Hamas or Hezbollah.
Even if Israel finds itself in a "deep underground facility", à-la Hal-Shifa, kind of scenario there is nothing that couldn't be done with an appropriate use of conventional GBUs.
As long as exit points are located, simply block them or collapse them, then just hammer down the whole complex.
Another scenario could be a decapitation strike. Again, Hamas, Hezbollah and their HVTs are not time-sensitive unlike, for instance, the Iranian Ayatollahs, the USSR Politburo, the US JCS, etc... Killing the leaders of these organization would not render these organization unable to function.
The use of B61 could, on the other hand, find a justification if used against critical Iranian infrastructures.
Israel does not need to "make a statement".
