After years of running Rrosetta@home I can no longer get tasks to download

Since there is no Rosetta 4.20 work to process (other than the odd resend or extremely brief burst of RB Tasks, and even rarer infrequent bursts of other Tasks), that's why you can no longer download work- unless you system requests some at just the right time.
There is plenty of Python work available, but it requires VirtualBox, and massive amounts of RAM & storage space. And even then, getting the Tasks to be processed (and keep working when new ones are started) appears to be problematic at best.