FWTW, some Israeli hostages released say that they had received less food toward the end of their captivity. E.g.:
They were not physically harmed and often ate pitta and cheese with their captors until food became scarce.
Or
While in captivity, she said the family survived on little water and food each day. “They tried to provide us with food. There was more in the beginning, but there was less later,” she said.
It's unclear though whether Hamas did this because they knew those persons were going to be released or they just didn't have enough to share. So, it's circumstantial evidence, like with much else in this matter.
Speaking of tunnels, the IDF did release some footage showing Hamas keeping some food and especially cash in some 'tunnels', or better said in the larger underground rooms thereof.

With cash they can certainly buy food on flourishing Gaza black market.
Every day, Yasser Bashir, another displaced person who is sheltering in a UNRWA school in the city of Khan Yunis, waits for more than two hours in a long line to receive his share of daily food aid, but every time he receives "a small amount of food that is not enough for just one person."
"They (UN organisations) deliberately humiliate us, and we do not get enough food or even water. In return, we are forced to buy it from the black market," the 54-year-old father of eight remarked to TNA.
But it's not clear to me if most Hamas units have loads of cash on hand, like in that instance. Netanyahu has recently claimed that Hamas mainly gets their food "at gunpoint", or at least that that's the main reason why there's not enough food getting to the average Gazans--which Netanyahu also says he doesn't have enough information on (i.e. that a food crisis is happening).
Hunger and malnutrition are widespread in the Gaza Strip. The United Nations warns that famine is imminent [...]. Responding to these claims, Netanyahu said: “We don’t have that kind of information. That’s not the information we have. And we monitor it closely.” [...]
Asked why more aid isn’t reaching Gaza by land, Netanyahu said: “Hamas is coming at gunpoint and stealing the food.
For what's worth it, (former PM) Naftali Bennett went further and claimed not only that Hamas is stealing loads of food, but that they are [stealing so much that they have enough] to be selling it back to the black market at 10x markup, i.e. that Hamas has cornered the food market!
And (I guess) to prevent that from happening, Israel has been bombing some UN food distribution centers, at least while there's a Hamas guy inside.
Israel said on Wednesday its airstrike on a U.N. food distribution centre in southern Gaza killed a Hamas commander whom it targeted, and Palestinian health officials said it killed four more people including a U.N. worker.
The Israeli military said the strike killed Mohammad Abu Hasna, whom it described as a Hamas militant who provided intelligence to the group on Israeli troops' positions and was "also involved in taking control of humanitarian aid and distributing it to Hamas terrorists." [...]
At least one UNRWA staff member was among the five killed and 22 others were injured, the agency said, adding that the facility's coordinates had been shared with the Israeli military.
Now, truth to be told, they hit him in the courtyard, from what I can tell form the video, and only 5 people or so can be seen in the IDF footage. A spokesperson for the Israeli government used the opportunity to remind that "UNRWA is a Hamas front that's running interference for Hamas abusing its UN logo".