I think all the plots I’ve posted on here (and other threads) have been produced on the pi directly. They aren’t particularly demanding, with the possible exception of the polar heatmap one, but that’s only if you feed it lots of data. The default settings will work fine on a pi 4. As for how to use them, most are a simple command line but occasionally have some dependencies that need installing to work. If you want to try something and get stuck you can always PM me or post on the Signal strength heatmap thread where most of my stuff ends up.
I also have a jupyter notebook running on that pi which is quite handy for messing about with data and producing plots in python. The pi 4 handles that fine as well.
As for getting the resulting plots off the pi, there are several ways. Some of the scripts will produce a web page output or put the resulting plots somewhere accessible via the browser. In that case it’s easy enough to just right click and save what you want. You could also use something like WinSCP to copy files via SSH or use an SSH client that has a file browser built in (eg MobaXterm). There’s a variety of ways to do it, but that’s probably the easiest.