Just tested some more and found that if you can figure out a reliable way (for your situation) to determine the next usable row, you can use Google Sheets Update a Row on that row and it will accept the colon in the sheet name.
If you’re adding multiple rows, start with the first usable and increment by 1 for each row update.
Here’s one way to get the last used column, just tweak it to get the last used row.