> Are we supposed to find the figurative "gym for problem solving" the same way office workers workout after work?

That's it, yeah. It sucks but it's part of the job. It makes you a better engineer.

You're absolutely right that this isn't sustainable however. In one of my earlier jobs - specifically, the one that trained me up to become the senior engineer I am now - we had "FedEx Fridays" (same day delivery, get it?). In a word, you have a single work day to work on something non-work related, with one condition: you had to have a deliverable by the end of the day. I cannot overstate how useful having something like this in place in the place of business is for junior devs. The trick is convincing tech businesses that this kind of "training" is a legitimate overhead - the kinds of businesses that are run by engineers get this intuitively. The kind that have a non-technical C-suite less so.