A 1:22 civilian-to-target ratio is not proportional. No matter how rationalize who the target is.
As best I can tell, there's no hard-and-fast established doctrine for determining weight of acceptable collateral damage.
But I'd point out that this guy is probably going to be considered a high-value target, someone that Israel would consider the loss of to have a disproportionate impact on the war relative to an individual infantryman. That is, losing him disrupts command-and-control.
Even if there were some firm number for warfare in an urban environment, like "1:5" or something, his value is probably going to be higher than that. Most countries aren't going to do F-16 strikes on an individual infantryman, questions of collateral damage aside.
It might be possible to look at the wargaming scoring rules that countries have used in wargaming exercises to try to get a feel for what militaries consider the "military value" of high-level figures relative to an individual soldier, and that might give some idea of what they might consider the ratio to be in a general sense. But my point is just that whatever the ratio is, it's going to be more than 1.
How many investigations have you heard of personally?
I mean, it's not really a topic that I'd personally follow. If it's typical of most countries, there are some, but soldiers tend to get the benefit of doubt, as they're in dangerous situations, and tend to be granted more leeway than someone in civilian situations are. That is, they aren't super-common, but do happen.
kagis
An Israeli military court has convicted a soldier of manslaughter for shooting and killing a Palestinian assailant who was already incapacitated.
The shooting happened in the occupied West Bank in March of 2016, and was captured on camera.
The judges found that 20-year-old Sgt. Elor Azaria acted in cold blood when he shot and killed Abdel Fattah al-Sharif, NPR's Joanna Kakissis reports from Jerusalem:
"Al-Sharif had been shot and wounded after stabbing an Israeli soldier. Eleven minutes later, Azaria shot the motionless Al-Sharif in the head.
But that just goes to the argument that they do happen. As to this particular situation, as I said in my prior comment, I do not expect that Israel will find the people who bombed the guy to have acted inappropriately.
It's kind of earlier, but a little bit would be casette futurism.
https://tvtropes.org/pmwiki/pmwiki.php/Main/CassetteFuturism
Amazingly, nobody appears to have done a Wikipedia page for cassette futurism yet, or I'd link to that.
EDIT: Here's a DDG link to an image search for cassette futurism, to sort of give an idea:
https://duckduckgo.com/?t=h_&q=cassette+futurism&iax=images&ia=images