Deleting Text Boxes
Adobe XD does not allow you to select and delete text sometime. Sometimes it allows you to click and edit and/or delete. Other time it doesn't. Inconsistent performance.
I wonder if some of what you’re seeing is due to a known issue about the keyboard not responding? The workaround for that is to change focus away and back to XD.
When you select a block of text it will usually either allow you to edit the text in the block. Or you can double click and delete the whole text block. I am working in Windows 10 and often finding that XD will just do anomalous things that are inconsistent or hard to replicate. IWhen you close and reopen the app it will work fine again, but this often causes you to lose unsaved changes in your work.