The Gaza Ministry of Health says as of today that 35,562 people have been killed [0]. The Israeli Ministry of Defense in March said it has killed 13,000 Hamas operatives [1].
Leaving aside the two month gap between these figures, the civilian casualty ratio is 1:1.7.
I tried to find a source for what a "typical" casualty ratio is in urban conflicts. This source [2] claims that 90% of overall casualties is a typical number. That would be a ratio of 1:9.
John Spencer, who chairs the Modern Warfare Institute at USMA, and seems to be an authority on the subject, has a tweet addressing this specifically [3], in which he cites the Battles of Mosul, and Manila as having casualty rates of 1:2.5, 1:6 respectively.
I don't think proving the negative of "lowest civilian casualty rate in modern history" is feasible, but a nearly 5x improvement in civilian casualties compared to the assumed norm, and lower civilian casualties than Spencer's comparisons seems to indicate that the claim is not without merit.
[0] https://www.aljazeera.com/news/longform/2023/10/9/israel-ham... [1] https://www.timesofisrael.com/liveblog_entry/hamas-says-gaza... [2] https://civiliansinconflict.org/our-work/conflict-trends/urb... [3] https://x.com/SpencerGuard/status/1786612914117349769