WHAT IS SUPPORTED
The distinction is formatting versus ink
Typed-text formatting stays attached to the words as you edit and move them. reMarkable officially describes bold and italic formatting for selected text, along with bullet points and checkboxes. It does not currently document manual strikethrough among those choices.
You can still draw a line through text with the Marker. That works as a visual editing mark, but it is handwriting layered over the page. It is not the same as applying a text style, and it may need to be moved or erased separately if the text changes.