When I got into IT, I had years of experience with Mac OS, UNIX, a bit of IRIX and VMS, BSD and even a bit of Linux.
And then I spent 10 years mostly managing a Windows shop. I still ran OpenBSD on the internal support servers, but had to support a full Microsoft stack for anything customer-facing.
What will increase your hiring chances is being adaptable and having a portfolio of success stories to reference during interviews.