I have an Infopath form that captures budget lines for different budgets in an SharePoint online list. The list captures the lines for each budget. There can be many budgets and then of course much more budget lines per budget. The total of this exceeds the threshold. The client came to the point where the form does not want to add more budget lines, because it exceeded the threshold. I've used indexing on the columns but is there another way to ensure that this will not happen again?
The item limit you're running into is the amount of items in a view (3000). Create a view that returns less than that. It can be a view that only shows lines for one budget. Or line items by category. You can have millions of list items in your list but, it'll only show 3000 at a time. So get creative!