This might sound like a cop out, but I run Pop OS (sorry to those who already know this from my other posts), which has a specific distro with NVIDIA baked in and working.
It upgraded to 460.73.01 automatically, just like any other auto update. I suspect, when it is stable and easily worked in, it will go to 460-80 and will work out of the box.
Just for those of us, like me, who are tired of trying to get NVIDIA to play nice.
Thank you to all for the replies. I’m still mulling about whether (or when) to take the plunge and upgrade; having potentially system-breaking changes held back by apt is a nice safeguard that I will only push past when I have a lack of time-consuming events. (Channels Aragorn from the Return of the King): Today is not that time, however!
I just upgraded my laptop to Kubuntu 21.04, which comes with kernel 5.11 and proprietary Nvidia drivers 460.80 (both pulled from the official Canonical repos). No problems, darktable runs fine with OpenCL enabled.