Install an app that monitors their usage (with consent of course). Run for a week or month. Justify with their own data. “You only actually do these 4 things. Let’s look at each of these good replacements for them” One at a time, gated. If 1 works, we move to 2, etc. When all done conversation is you like these 4 now, they all run on Linux, let’s backup all your files and switch to Linux. You’ll have all your programs, and the files you need. And we’ll start with a skin closest to macOS look and feel.