So the person never does anything outside of his employer's IP? That's unfortunate, but as a heuristic, I'd like to see stuff that the person has done if they claim to be in a field.
Perhaps other people don't care, and will be convinced by expertise without evidence, but I'm busy, and my life is hard enough already: show me your code or gtfo. :-)
Also, unless you are in CA many companies have extensive IP assignment clauses, which makes moonlighting on other projects potentially questionable.(especially if they are assholes)
My previous job made it hard to even submit bugs/fixes to open source projects we used internally. Often we just forked b/c bureaucracy (there's a reason it was my previous job)
Not saying your wrong, seeing someone's code is nice. As long as you are aware that you are leaving alot on the table by excluding those that do not have a presence. (Particularly older with kids)
The process for me to submit a PR to an OSS project at my last firm took so long that by the time it got through legal review and I was authorized to see it through to the end, it had been 1.5 months and I went from having some free time to work on it at work to being swamped with work doing hardware bring-up and leading a massive redesign project.
Someone who worked on successful projects that shipped and are still out there, they can point you to that. You can buy the app, or device with their embedded code, or use the website or whatever. Not always an option for everyone, or not all the time.
That's one reason why there are skill tests in interviews. And why people ask for, and contact, references.
Public code can't be trusted. If you make that the yardstick for hiring people, then everyone and his dog will spin up some phony github repo with stuff that can't be confirmed to have been written by them. Goodhart's Law and all that.
You have no idea how much help someone had with the code in their github repo, or to what extent it is cribbed from somewhere else. Enter AI into the picture now, too.
If they can't I give the option to write some code that they like and they think shows off what they can do, usually suggesting to spend half an hour or a couple of hours on it.
To me it's an obvious red flag if there is nothing. It's as if talking to a graphics designer or photographer and they're like "no, sorry, I can't show a portfolio, I've only done secretive proprietary work and have never done anything for fun or practice".
Those that show me something get to talk about it with me. A casual chat about style, function, possible improvements and so on. Usually when they have nothing to show they also don't put in that half an hour to make something up, or get back with excuses about lack of inspiration or whatever, and that's where I say "thanks, but no thanks, good luck".
If you can't easily initiate a git repo and whip something up and send it to me in half an hour you won't be a good fit. It means you aren't fluent and lack in experience. I might consider internship, or a similar position where you mainly do something else, perhaps you're good at managing Linux servers or something but want to learn how to design programs and develop software as well.
And frankly, when you hire a manager or executive, there's not generally a single artifact that you could use to examine their value-add. You can see perhaps the trajectory of a company or a division or the size of their team over time, but you can't see the pile of ongoing decisions and conversations that produce actual value.
I think the flip side regarding code is, the stuff I do for fun outside of my employer's IP is not at all representative of what I do at work, or how. I pick topics that interest me, work in languages that my company doesn't use, etc, and because my purpose is learning and exploration, often it doesn't end up as a finished, working, valuable piece of tech. I deliberately don't do anything too close to my actual work both b/c that just feels like working longer and because I'm concerned it would make ownership of the code a bit fuzzy, and perhaps it would be inappropriate to consider open sourcing. Because my side projects are eclectic and didactic, I rarely put it in a public repo -- but it has served its purpose of teaching me something. If I shared all of my code side projects, they would show an unfocused person dabbling in a range of areas and not shipping anything useful, because that's what's fun ... whereas at work, I am focused in a few quite narrow areas, and working on customer-facing features, because the point is to build what the company needs rather than what I enjoy building.
The main difference between those professions and people who build software for a living is that they have organisations that predate modernity that keep tabs on their members and kick them out if they misbehave.
We should absolutely build such organisations, but there will be intense confrontations with industry and academia when we try, because capitalists hate when other people unionise and academics think they're the best at evaluating peers.
It's fine that your personal projects aren't polished products. They show your interests and some of how you adapt to and solve problems. It's something you've chosen to do because you wanted to, and not something you did because you were pressured by profit. The everyday grind at work wouldn't show what you'd do under more exceptional circumstances, which is where your personal character and abilities might actually matter, but what you do for fun or personal development likely does.
We simply cannot tell that.