Why can't I find the Google Sheets action in my automation rule?

It is not hidden, it only exists one step up

systeme.io's article on the Google Sheets integration says so directly. The action Add a new row to a Google Sheet is only available inside Workflows, and it is currently not possible to do this with a plain automation rule.

systeme.io's own workflow guide lists that same action among the ones a workflow step can run, in the same list as sending an email or adding a tag. Its automation rule guide, covering the same kind of step, never mentions it. The two articles agree with each other without either one saying so directly.

Two things have to be true before the action even works

First, a Google account has to be connected. Profile picture, then Settings, then Integrations, then Google Sheets, then Connect, then choose the account and allow systeme.io to see, edit, create and delete only the specific Drive files used with it. More than one Google account can be connected at once.

Second, the worksheet needs its column headers already in place before you pick it. systeme.io states plainly that the current integration cannot create a brand new Google Sheet from scratch, only add rows to one that already exists with headers.

Where to actually build it

Automations, then Workflows, then + Create. Add a trigger from the + Add a trigger box, add a step, and choose Add a new row to a Google Sheet as the action. Pick the connected drive, then the specific sheet, then the worksheet inside it, then map each piece of data to a column. Two different fields, first name and surname for instance, can be mapped into the same column.

Run the test in the Tests section before trusting it. systeme.io's own example shows a fresh row landing in the sheet after the test runs.

One more restriction, if someone else runs part of the account

Only the account owner can create or edit this integration. systeme.io states the change is disabled for Workspace assistants specifically, for what it calls better security and exclusive control over the connection.