Update
Support has been helping me with this issue for the past week and I just received a solution. I’m posting about it here in the hope that it helps anyone else who is having this problem.
If you can’t zoom with your mouse scroll wheel & you are using Windows 10, go to your Windows Settings > Devices > Mouse, and check if you have the ‘Scroll inactive windows when I hover over them’ setting enabled. If it is disabled, enable it and try to zoom with the scroll wheel again in Harmony.
Enabling this setting solved the issue for me. I think it must be a bug, because I’m able to zoom with the scroll wheel in Harmony 21, 20, & 17 even when the ‘Scroll inactive windows when I hover over them’ setting is disabled. I believe something must have changed in Harmony 22 which causes an issue with this setting being disabled.