In my own experience... Windows MC is the 'fastest', Linux MC is second and Mac MC is the third. But there's some things Mac MC is better at versus Linux MC and vice versa.
I can see clearly on this old machine not only is JRiver obviously a Windows program later ported to macOS
Not exactly, the performance issues on Mac likely have to do with the way MC renders the UI - for example non-Retina Mode MC performs better than MC in Retina Mode. With Retina Mode enabled, MC looks great on Mac, but the handoff is worse performance (e.g. scrolling is bad, but tolerable if you're music-only) so I run MC for Mac in non-Retina Mode currently. Otherwise MC is a cross-platform application compiled for Mac. Try reading this topic for more insight to why Mac MC is 'slower' versus Windows/Linux MC, especially Hendrik's posts;
https://yabb.jriver.com/interact/index.php/topic,111729.0.htmlIt's not an easy thing to fix, unfortunately. Hopefully eventually it is fixed and MC for Mac's performance is as fast as Windows and Linux... or at least Linux, which is pretty good already, IMO. I don't think MC for Linux suffers from the same issue(s) with UI rendering. If it does, I've not noticed it at all. Personally, since MC 23 for Linux and Mac is pretty close to "feature" complete (at least of the major stuff) for the MC 24 development cycle I'd like to see performance improvements to Linux and Mac being one of the main focuses, including fixing the rendering performance issue(s) on Mac.
and not only are there some features on Windows side that don't work on macOS, but it also just plain runs better / faster in Windows.
It'll also apply to Linux too in addition to Mac vs Windows. This is an ongoing thing development-wise actually as the 'missing' features are slowly being added to Mac and Linux builds of MC. It's not a simple thing to do as Windows MC uses things like Direct3D, DirectShow, etc. whereas those are not available on Mac and Linux and need to be developed from scratch (if possible at all, some things aren't, e.g. things like madVR). But it's a lot better now than it was a couple years ago - MC for Linux/Mac 23 supports video playback, image support, Theater View, etc. There's still some missing stuff, e.g. television support which *may* not even be possible on Linux and Mac.
is performance any better or worse under Linux compared to macOS?
In my own testing, Linux MC is the second 'fastest' and Windows is the first.
anyone migrate a JRiver library from macOS to Linux? I have moved a library from one Mac to another, and that was successful after an initial misstep. I know mac & linux file paths are much more similar than under Windows. But I am sure there are issues that would arise, and maybe it wouldn't even work at all.
This is where you're going to run into issues. Even though paths on Mac and Linux are similar, for example by default mounted volumes are located in different locations. I suggest you use the Rename, Move, & Copy Files tool and read the Wiki about moving files:
https://wiki.jriver.com/index.php/Moving_FilesIn addition if you're using a NAS or an internal/external hard drive to store your media files the file system itself might be an issue. If you're using HFS+ or APFS you will likely run into issues on Linux - there's no APFS driver for Linux and I'm not sure if HFS+ partitions can be written to in Linux either, never tried. If you're using FAT32 or exFAT, you should be fine. If you're using NTFS, you'll likely need to use ntfs-3g for best results on Linux.