I have seen some leftists stand by this statement as entirely true, and I have also seen some leftists dismiss this idea as cope on the part of liberal Zionists who dislike Netanyahu/Likud (and who would like to delegitimize both Likud and Hamas together).
The following are some relevant articles that support this idea:
https://www.timesofisrael.com/for-years-netanyahu-propped-up-hamas-now-its-blown-up-in-our-faces/amp/
https://theintercept.com/2018/02/19/hamas-israel-palestine-conflict/
https://www.thenation.com/article/world/why-netanyahu-bolstered-hamas/
What is clear is that Israel has allowed Qatar to fund Hamas on numerous occasions without much interference. However, whether Israel has ever actually funded Hamas specifically with Israeli money is not as well-established (although many of the people who support the general “Israel propped up Hamas” idea definitely imply that this has happened). So as a corollary question, how important of a difference is this?
It might be more accurate to say Israel propped up Hamas through various channels (including Qatar) as a general strategy of undermining the Palestinian Authority and split Gaza from the West Bank. "Supported" can have many different meanings that don't require direct Israeli government funds. To me, this sounds like classic blowback to Western meddling, and whether Israel directly funded Hamas is a red herring.
It's like the phrase "The CIA used drug money to do XYZ" is less of a mouthful than "The CIA manipulated ABC regional politics and XYZ violence such that the drug trade benefited allies and harmed opponents of the CIA."