Old iMac. How do I revert to pre-CR 17.0.1?

Been merrily editing my CR3 files with Camera Raw (don't know what version) until today, when CC auto-updated to CR 17.0.1. Now: I'm dead. 

I updated to the latest OS that my 3.3 GHz Quad-Core Intel Core i5 will run: 12.7.6.

Still not good.

How do I revert to an earlier version of CR that plays nice w OS 12.7.6?

Obviously, I need to get a newer computer. But for now, can I get some time-travel help? Thanks.