I know for sure several airports are using OpenVMS, and there are more we don't know about, as some companies keep running yheir stuff for decades not asking anyone for support.
And I'm sure There are multiple other old systems out there, it's too hard to replace them.
And they work! Our VMS stuff runs great, it's fast, and the uptime is measured in decades sometimes. So the problem is hardware: we rolled out the first production x86 version this year, so our users are fine (it's still an issue of porting your software, but it's not as terrible as building everything from scratch), but before that OpenVMS could run on Itanium servers at latest, and the platform was dying off since the beginning of 2000s, so it is a problem to find a normal replacement machine now.