BusyCal 2022.3.1 adds support for creating automation rules that allow you automatically categorize / tag incoming events.
Each account added to BusyCal can have its own set of automation rules.
To create a new rule, open BusyCal Settings > Accounts and then select the account you wish to add one to.
Next, click on the Automation tab.
Here, you can enter the tags you wish to automatically assign to incoming events. Only events that are pulled from the server during sync will be automatically tagged.
If you have multiple rules, you can drag the rule to change its position to influence its execution-order. The following additional options can be enabled for each rule:
Assign To "My Tags": Enable this to add tags to "My Tags". "My Tags" are only visible to you and local to your mac. These do not sync as part of the event. Read-only events will always have tags added to this field.
Stop processing more rules: Enable this to stop processing additional rules in case this one succeeded in tagging the event.
Auto tagging, automatic tagging, auto categorize, categorise, categories, auto-tag, auto tagging events, auto tag event