I can see the value of feature not to backup when ransomware has been detected. This so your backup won’t be contaminated with files you do not want in your backup.
However, you would probably want the backup to run despite it being overrun by ransomware, because you might save files that have changed between the last backup, but haven’t been corrupted yet by the ransomware…
A few years ago our compaby was attacked by ransomware, our sales database was about 60GB, because of the cheer size, the ransomware had not encrypted the file when we discovered the infection. If we had been to late, I would have liked my backup software to have backupped our database.
BTW I never understand why the suggested anti ransomware could not be added as an option.
So people could choose how Duplicati should react when detecting ransomware.
We live in a world of individual choices now!
You would like it when your supermarket decided you were ony allowed to eat peanutbutter on your slices of bread ?

*** the above is not an attack, but I believe in giving people choices and working towards solutions instead of talking about why not to solve a problem ***