I'm only suspicious if they don't simultaneously and eagerly show me their Github so that I can see what they've accomplished.
Sometimes this industry is a lot like the "finance" industry: People struggling for credibility talk about it constantly, everywhere. They flex and bloviate and look for surrogates for accomplishments wherever they can be found. Peacocking on github, writing yet another tutorial on what tokens are and how embeddings work, etc.
That obviously doesn't mean in all cases, and there are loads of stellar talents that have a strong online presence. But by itself it is close to meaningless, and my experience is that it is usually a negative indicator.
Actually it is incredibly difficult, because you no longer have access to your previous employers' code bases and even if you do, it is illegal for you to show it to anyone.
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. :-)
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.