Thank you for sharing a screenshot of what you're seeing on your screen, c-campbell. It could be that you have too many columns on your estimate table.
When you have too many columns to fit in the screen, QuickBooks Online adjusts the view by adding a long gray side-scroll bar. You just have to drag it to the right to see the three dots mentioned by KayePe.
Here's a screenshot for reference:

If the same issue happens, we can do browser troubleshooting steps related to cache. It is a component that is being accumulated as we use our regular browser. Cache helps the browser load the details we are commonly accessing. However, cache can also cause unexpected behaviors on the browser if it stores too much of those.
Let's start by using a private browser. It doesn't store cache like the regular one. Here are the keyboard shortcuts we can use depending on the browser you're using:
- For Firefox, press Ctrl + Shift + P
- For Chrome, press Ctrl + Shift + N
- For Safari, hold down Command + Shift + N
If you can delete the line item successfully, we can clear the stored cache on your regular browser. Otherwise, we can use a different browser aside from the one you regularly use.
After you edit the estimate, you can already convert it to an invoice. Then, record the payment once the customer pays it.
Keep us posted on how the editing an estimate goes so we can give you a hand if you need additional assistance.