It seems like Unity or the asset store has changed how they work. When I try this with 2019, I still get packages that were loaded with versions that are older. This is an error on Unity's side, because I have the compatible package uploaded with unity 2019, it's just not getting downloaded. What you can do to get the old version, that is compatible with 2019, is to add this to your manifest.json "scopedRegistries": [ { "name": "Rain Office", "url": "https://office.rain-games.com:4873", "scopes": [ "yamldotnet" ] } ], The package manager should then suggest the 6.1.2 version to you. But this package doesn't have examples, and it isn't referenced by the default assembly, so you will have to manually reference 'YamlDotNet.asmdef' to be able to use it. You can probably steal examples from the new package (on asset store, or downloaded with newer 2020.3 Unity). I hope that helps.. at least in theory you should be able to work around the asset store and use YamlDotNet with 2019 this way.

This is the last that I heard of it. https://github.com/aaubry/YamlDotNet/issues/140 So basically... Unity doesn't follow the yaml standard precisely, and accommodating it without breaking the library isn't trivial. So you will have to prefilter the unity-yaml a bit before you can work with it. Not very satisfying, I know, but it's the state of YamlDotNet and Unity at the moment.

This package is a free convenience version of the YamlDotNet free and open source library. It can do standard YAML, but sadly, Unity has been outputting non-standard YAML lately, and so the library might be insufficient in certain use cases if they involve assets produced by Unity. For that I can only apologize.

It seems like Unity or the asset store has changed how they work. When I try this with 2019, I still get packages that were loaded with versions that are older. This is an error on Unity's side, because I have the compatible package uploaded with unity 2019, it's just not getting downloaded. What you can do to get the old version, that is compatible with 2019, is to add this to your manifest.json "scopedRegistries": [ { "name": "Rain Office", "url": "https://office.rain-games.com:4873", "scopes": [ "yamldotnet" ] } ], The package manager should then suggest the 6.1.2 version to you. But this package doesn't have examples, and it isn't referenced by the default assembly, so you will have to manually reference 'YamlDotNet.asmdef' to be able to use it. You can probably steal examples from the new package (on asset store, or downloaded with newer 2020.3 Unity). I hope that helps.. at least in theory you should be able to work around the asset store and use YamlDotNet with 2019 this way.