hi @M_G , welcome to the community. I can see why this feels difficult, Coda is a different concept compared to any spreadsheet. Getting access to the previous row logic is not that difficult, you can have a look at this blog, it shows an easy way out.
in a formula that results in the filtered output (on canvas, in your column, in an automation)
in a formula applied to the view of the table resulting in a filtered view (related to the output)
Indeed, both are unrelated and I would like to see this different.
when you want to have the outcome of the filtered view, you have to recreate the filter in your canvas function in the same way. you thus create a filter to get a different table view and you create a filter on the canvas that gives the related outcome.