How are you merging the data from multiple tables? Could you add the type at that point?

@ktosiek i could do it with some js in the client yes, just wondering if there is a neater solution

You could also add a column with default = 'my-activity-type', or even use a virtual column (see https://postgrest.org/en/stable/api.html#computed-columns, you could have an

activity_type

function for each table that can be used as activity)