Ok, so first of all sorry if this post is all over the place or does not make perfect sense. Honestly my head is all over the place about this. I am by no means an expert, but I make do.

I have some old code that targets .NET framework 4 and I would like to start down the path of developing a "companion" style mobile application for some of my users. The idea is this would be a bare bones app that runs on a handheld device that has the capability of performing a select few of the lighter tasks that can be done with the full desktop software.

My question is about upgrading the framework on these older class libraries to something that can be referenced by a UWP application. I understand that they need to be .NET Core (Standard?) libraries and that .NET 4.5+ should implement that? Does that mean I should just make these libraries target 4.5 since that is the minimum or do I go for the latest? Should I be targeting one of these Core frameworks instead? My guess is that upgrading the class libraries would also require me to upgrade the windows forms applications that reference them. Will windows forms still support the upgraded class libraries? Thank you in advance!