I freelance. Occasionally I get called by former clients to work on legacy systems I was lead on. And I have some support tasks for former clients.

For one company I log on once a month, I start a Renovate process which generates pull-requests for updated dependencies. Patch-versions get auto-merged after tests succeed, minor and major need approval of the current lead. Sometimes I need to manually tweak the code a bit because of API changes or to get tests to pass. I'm allowed to bill them four hours on it regardless of actual work, which is between five minutes (no manual intervention required) and two hours (need to rewrite some code).

For another company I create a report once a month for all outages and which errors frequently show up in logging. I automated this to be a five minute task and it generates a Wiki page. I review the page to see if everything is ok. I bill an hour on this.

The company is happy to not have to allocate engineer hours on maintenance so they can continue pumping out new features.

I'd say that on average I work 4 hours and bill 12 hours. This is comparable to the income of someone in employment working around 24 hours. But I do run a significant risk obviously.