I'm still confused on what your saying. If a public official wins a § 1983 suit under a qualified immunity defense, there are no monetary damages to be indemnified against. Their employers only have to indemnify them if it is found they did not have qualified immunity and then had a judgement against them.

Are you saying that, for practical purposes, qualified immunity doesn't matter to the individual as they will almost always be indemnified anyway? I suppose this is true in a pragmatic way, but not in theory. As you say, there's no law that says the government agency has to indemnify. While I'd be surprised to find a case where the official ended up paying anything out of their own pocket, there are plenty of cases where the official has lost their job over a judgement against them and none that I could find where they won the case due to being covered under qualified immunity but still lost their job over it.