There's a quiet frustration buried in this question, and it's one we've all felt when a tool promises flexibility but delivers friction instead. The user isn't asking for much: a locked-down Excel Online sheet where people can still type into A1:M1000, filter those columns, and delete a row by selecting it and pressing the delete key. That's it. But the moment you try to protect the rest of the sheet, the whole thing unravels. Lock the sheet, unlock the range, and suddenly row deletion stops working. Unlock everything, and you lose control. It's a classic trade-off that shouldn't be a trade-off at all.
Here's the thing: the user's instinct to lock the entire sheet and then unlock A1:M1000 is correct in theory, but Excel Online treats "delete row" as a structural action, not a content action. When a row is selected and deleted, Excel wants to remove the entire row structure, which is exactly what you've told it it can't do. So the lock holds, but the feature breaks. The workaround is to stop thinking in terms of rows and start thinking in terms of ranges. Instead of letting users delete entire rows, give them a clear path to clear the content within the allowed range. Select A1:M1000, press delete, and the data disappears. That's not a compromise; it's a better fit for the constraint you're actually trying to enforce.
What this means for you, practically, is that you have to choose between two things: allowing structural changes to the sheet, or allowing users to delete data. You can't have both in Excel Online without a script or a more powerful backend. But you can have the next best thing. Set up your sheet with a locked range, keep the filters on, and accept that "delete" will mean "clear contents" rather than "remove the row." If you need the row to disappear entirely, you're now in the territory of Power Automate or a custom script, which changes the scope of your project. That's not a failure of your approach; it's just the boundary of the tool you're using.
The real takeaway here is that Excel Online's protection model is built for content, not structure. It wants to keep your formulas and labels safe, but it wasn't designed to give you granular control over row-level deletions. So stop fighting it. Lock the sheet, unlock A1:M1000, and train your users to select the range and press delete. It's not as elegant, but it's reliable, and reliability beats elegance when you're managing a shared workbook. If you truly need row deletion, you need a different tool, but for most data entry scenarios, clearing content is enough. That's the honest answer, and it's the one that will save you the headache.