windows – Bootcamp-ed Mac Pro 5.1 — Boot keyboard shortcuts no longer working

I’m really hoping I can get some help with this issue. I’ve bootcamped my 2012 5.1 Mac Pro with Mojave on one end and Windows 10 on the other. I’ve also upgraded my GPU to an RX580 from MacVidCards with the Apple EFI mod.

Everything went well for a few months until about a week ago when using Windows I restarted and tried using the option key method to access the boot screen and select my Mac drive. It simply ignored the key press and loaded Windows instead. In fact, I’ve tried many of the keyboard shortcuts for different boot options (CMD+R, CMD+Option+P+R, etc.) to no avail. I’ve made sure to press the buttons at the right time and all that mess.

I’ve spent the better part of last week searching for any sort of answers, but nothing seemed to fit my situation. Hopefully it’s something simple and sweet!

Thanks for any and all help!