It can raise doubts and suspicions with employers though. Why wasn’t he employed? Does he have a problem with work? Was he in jail? etc. Even if misplaced, you, can’t stop people thinking that way
Thing is, you don't need every job, you just need one job. It's not hard to find teams that are reasonable and don't get obsessed over traditional "red flags" that actually carry almost no useful signal.
If your company is working with outdated software, or ignoring software best practices like testing or security, or even if you've just started to specialize in a very narrow way, it can sometimes be difficult to translate the skills you're using there into other companies.
It's very common for people to start to specialize the longer they work at a company. You can end up knowing a few things really well, and not much else.