SharedGL was enabled by bug 1535893 for wayland.
This has resulted in peculiar flickering when multiple windows are present. On Sway, this is seen as an odd surface extending from the right and bottom edges of the window, which seems to toggle on/off every time the cursor moves a pixel.
It is most easily seen to be covering the status bar if set at the bottom, and due to my configuration of Sway forcing a 10px gap around all windows, it can also be seen covering the background on the right of the window.
Other surfaces also sometimes end up flickering, such as context menus or web extension overlays.
Testing shows that the issue was not present prior to merging bug 1535893, but is present after.