I have 2016 v3. I know I can't get updates but I CAN build OS X projects. When I check Windows, it says I need a build license. So why one and not the other.
It really depends on what you need. Your license is expired, if you only need Windows going forward you can get a Xojo Lite $99 - Windows license and build apps for Windows-only. If you do need cross-platform, look at the $299 Xojo Desktop license - with that you can build for macOS, Windows and Linux. You can view all of the options in the store .
I don't know if I'm 100% sure, I just started learning Xojo.
With a $299 license:
Am I right?