Scheduling and managing events using Outlook.com calendar
I have the same issue. First it started on my laptop and now it's also on my desktop. The ability to add icons is still there, but the UI doesn't show them (I honestly cannot believe Microsoft would have such an ugly experience, either leave them or take them off completely, showing them blank just leads to you to think it's a bug, not a feature change).
And yes I tried clearing cache and even open the Calendar in incognito, no success! :-(
I only use Outlook web, I don't use the desktop version as I only use the Outlook Calendar not the email management, but those icons we heavily relied on. We are a bookkeeping company, every work we do is schedule on Outlook Calendar. The icons helped us identify work types which were "do not disturb", meetings, out of site or away on holidays. We used both icons and colours. I cannot believe they have been removed! So annoying!