Ok, so I've found a lot of information but a lot is stratified and can be somewhat confusing, so I'm going to post what I have found and also ask for any other suggestions. It's not uncommon for cheese grater Mac Pro users to have no boot screen these days. They allow us to use a bevy of great graphics cards, but sacrifice the boot screen unfortunately. This creates some problems if you have Windows installed. I have recently updated to Mojave from High Sierra, but both have a similar issue. Basically you can get into windows easily by going through startup disk in System preferences over on the macOS side, but the bootcamp help tray can't find macOS to get you back. As per this support document (https://support.apple.com/en-us/HT208123) HS and Mojave for some reason do not support the tool with APFS volumes, instead requiring the boot switcher. This seems to expressly target Mac Pro users without boot screens and intentionally make their lives more difficult. Grumble. As of right now, there are 2 main ways to get back to macOS: You can 1) reset the NVRAM/PRAM with option command p r. This takes several minutes, but it will default back to your macOS drive for booting. Or, 2) you use the boot switcher without seeing it. Basically hit the power button and when you hear the chime hold alt, then wait like 30 seconds and tap an arrow key once (assuming you only have 2 boot volumes), and you should switch. This is pretty hit or miss. This is what I've gathered and discovered while experimenting with my 2010 Mac Pro, if anyone has a better method (these are admittedly terrible) I, and probably a lot of others, would find it very helpful. Thanks!