Browsing my /var/log/dpkg.log history, it looks like mine was 4.2.1.102+dfsg2-7ubuntu4 which seems right even today for Linux Mint 18.1 which derives from Ubuntu Xenial Xerus (16.04LTS) and uses its packages.
and I’m not sure if you normally use OneDrive, but if you do, you’re not having the above issue somehow. There have been reports of failure, and they probably don’t need another, but success may be interesting.
Upgrade the Mono version to 5.x is a Ubuntu issue citing the same (temporary) technical issue Fedora hit, then the update got in Ubuntu 19, someone’s asking about 18.04 LTS, and I suspect 20.04 LTS will have it.
I think it comes down to a question of how far Duplicati can ask the typical user to upgrade their system or their mono (which would risk their system, e.g. by dragging in some new dependencies that break things).
Actually doing the “ask” is another challenge because Duplicati’s updates don’t know about dependencies. Initial install does (at least on some OS versions), but that’s done once. Update drops in, and runs (or not).
Though this survey is probably far from random, I’m interested in what people think of upgrade challenges.
As per discussion in another thread, I just realized that I don’t actually know which program to check to answer your question.
I have installed Duplicati2 for the first time in september 2017, and I checked the installation instructions only back then. Afterwards, I have not looked for updates. Now that I did, I learned that you require us to install mono-devel, not something called mono.
When I answered your question, I gave the version of mono, and ignored mono-devel. I have not installed or upgraded either of them, so I have for both the version that comes with Ubuntu 16.04. Apparently, the mono-devel version is recent enough for you (but mono is not).
This goes to show I had no clue of what mono is. Might I be the only one here?