Hello,
According to these release notes, Categories now support Custom Attributes. My question is how do I add Custom Attributes to my Categories using the website or POS? The UI doesn’t show a way to add them. Any ideas? Thank you
At this time you’ll need to use the API to add custom attributes. 
Hello. Are there any plans to finally getting this feature added to web portal or POS? Thank you
Unfortunately, we don’t have public roadmaps for feature request like this. The team is aware of the request and will prioritize accordingly.