When I first started using Linux in 2022, I did it exactly that way - bought a separate drive, installed that OS on it, and then whenever I booted my computer I could choose which OS I wanted to use. I had that separate Windows install hanging around all the way up until just last month actually, when I finally got rid of it and repurposed that drive, and I felt comfortable doing that just because it had been close to a year since the last time I'd really *needed* to boot Windows for anything, other than keeping Windows itself updated. But yeah, it's super useful to have around, especially at the beginning when you're just starting to dip your toe into Linux.
In fact, it's probably really the only safe way to have both. I have seen reports from time to time that if you try to install both Windows and Linux partitions on a single drive, they'll tend to fight - often Windows will do things that just break or even flat out delete the other partition.
