Hi @rolando
Welcome to Q&A forum~
> is it expected that after a few seconds of typing, the text gets "locked" and you are not able to delete any marked text when using backspace?
No, you can use Backspace to delete, unless it is marked as deleted content like the highlighted text in following image.

For better analysis, could you please take a screenshot and share with use to show more details of your issue?
Besides, you can perform Online Repair for Office in Control Panel.
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