After installing Ubuntu MATE 21.10, fresh install on a virtual machine, I can see that clementine, vlc, steam icons seem to behave correctly out of the box. All icons seem to be properly scaled.
Version of indicator applet complete is 1.26.0
I installed per your request libayatana-indicator 0.8.4-1ubuntu1 and its dependencies, and restarted the VM. Still everything looks scaled well and without issues.
After installing Ubuntu MATE 21.10, fresh install on a virtual machine, I can see that clementine, vlc, steam icons seem to behave correctly out of the box. All icons seem to be properly scaled.
Version of indicator applet complete is 1.26.0
I installed per your request libayatana- indicator 0.8.4-1ubuntu1 and its dependencies, and restarted the VM. Still everything looks scaled well and without issues.