2.0.8.1 runaway memory consumption

Do you mean it increases while idle, or it remains high when idle?

Is there a backup or other work ever done? To what storage type?

Is Remote volume size on Options screen still at 50 MB default?

is similar to this, and you can look over the questions from there too.

This might also be a mono problem. If so, mono’s going away soon…
The current testing versions of Duplicati are replacing it with .NET 8.

What’s your mono --version number? Note mono’s pretty stagnant.