Release: 2.0.6.2 (experimental) 2021-05-29 is out with what is believed to be a workaround for the mono bug that broke SSH.NET that broke Duplicati. ECDSA host keys will not be used in mono until supported.
@Rob_Canada and @ghysler (and any others who saw this) are invited to remove workarounds from servers, and test it out. It should be safe to stay on, as it has only two changes from 2.0.6.1 Beta release, however you can set the Update channel back to Beta if you prefer to avoid future Experimental releases. Experimental is currently used as last step before Beta, so this code will probably be next Beta after test.
If you generally upgrade from Duplicati autoupgrader, you can go to Settings and change Update channel from Beta to Experimental, and it should offer this upgrade. If you prefer, installing manually will also work.
For best testing, please go to the Destination screen Advanced options, delete any ssh-fingerprint option, then use the Test connection button to accept a new one. Remember to go to final screen 5, to save it.