The disease choices are "hardcoded" so Covid-19 won't appear (if ever) until an updated client is released. "Any" is the correct choice which lets the assignment servers select your work units based on what is available.
There's lots of good information at https://foldingforum.org/ but in a nutshell, it appears that new clients are signing up faster than they can get new work units generated so many clients (new and old) are seeing no WU available.
Got exactly one work unit today, and have one on 'waiting to send results' for a couple of days already. There are definitely too many clients available now
Finally got my assignment. It took about 15 hours or so from the time I downloaded FAH. Of course, like a dummy I shut my machine down last night, rather than leaving it running. I'm making up for some lost time by turning it up to full folding power now. (I don't mind the CPU load when I'm just catching up on emails.)
If you're not getting F@H work units, try installing Rosetta@Home that's doing the same sort of thing: Join Rosetta@Home.
I have both clients running - when I have a F@H WU it takes the lion's share of the CPU and all the GPU, when I don't have a F@H WU Rosetta kicks in to do work.