Audacity is the only app that is this bad (I run KDE; my entire desktop is Qt5 so clearly that is not comparable).
I've noticed that the Audacity issue seems proportional to the number of tracks (not how much of the screen they take up) and improves when I zoom in a lot (to the sample level), which tells me this isn't a simple pixel pushing problem but rather something more profound in Audacity. There is obviously something horribly inefficient about how waveforms are being drawn at lower zoom levels.
For comparison, I can run full-screen Ardour with an order of magnitude more tracks and complexity than Audacity and it still performs much better, even if it isn't perfectly smooth.
I've noticed that the Audacity issue seems proportional to the number of tracks (not how much of the screen they take up) and improves when I zoom in a lot (to the sample level), which tells me this isn't a simple pixel pushing problem but rather something more profound in Audacity. There is obviously something horribly inefficient about how waveforms are being drawn at lower zoom levels.
For comparison, I can run full-screen Ardour with an order of magnitude more tracks and complexity than Audacity and it still performs much better, even if it isn't perfectly smooth.