What kind of devices are supported/required to run builds using .NET 4.x scripting runtime?

I'm currently targeting Android and iOS using legacy scripting runtime (.NET 3.5 equivalent - .NET 2.0 subset).

During my research I got the impression that changing the runtime (to .NET 4.x equivalent - .NET standard 2.0) will allow me to use more APIs and libraries at the cost of having fewer devices to target.
However, I can't seem to find how such a change affect the devices or even what determines whether a device will be compatible with the new runtime or not.

• I've seen the table from this page, but I'm confused as to how a particular Xamarin version's compatibility translates to what Android/iOS version I can target by using .NET Standard 2.0 : https://docs.microsoft.com/en-us/dotnet/standard/net-standard

• Here it's even stated that "Fewer Android devices support V8.0 than V7.0, so there’s also a tradeoff: access to more APIs or to more devices", but what constitutes those said devices https://blog.xamarin.com/history-dot-net-standard/

• And in this page it is stated that Unity "has committed to supporting this profile across all platforms that Unity supports", but again, starting from which version? https://docs.microsoft.com/en-us/visualstudio/cross-platform/unity-scripting-upgrade?view=vs-2017

Can someone enlighten me on this?