'Secure boot violated' AND Unable to enter BIOS!

I've been running OSx on a purpose-built machine with an Asus Z97m plus mobo for over 8 years. However upon recently upgrading to Catalina, I can no longer enter the bios (black screen every time). In a subsequent effort to do so, I removed and replaced my CMOS battery, and now of course that the default bios settings are back, I get the error that I'm not booting to windows (secure boot violated)... Yet since I am unable to enter bios, I am at somewhat of an impasse! 🤦‍♂️

What should I try? Could I make progress if I created a bootable windows volume? I actually intend to turn this machine over to Linux, but either way I need my bios!

All assistance welcome 🙏

submitted by /u/trawkus
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