Wave display cursors have blue box behind them

Device: Chromebook, with ChromeOS up to date
Linux version: Debian 12.5 (Bookworm) up to date

Problem: the cursor when moved over the waveform display changes to the same cursor but with a solid blue square behind it. When the cursor is moved to other places on the screen (menu bar, track properties, i.e. anywhere but over the wave) it’s back to normal, no blue square.

These have no effect:
– restart Linux container
– start Audacity in new Linux container
– delete audacity.cfg and restart it

It looks like the cursor sprite background transparency is not happening when over the wave rendering. Happens over both the wave and spectral displays.