Turning wrap lines on and off is a little different to pasting lots, [...]
In FeatherPad I didn't turn on and off 'Wrap Lines', I did the test from https://github.com/geany/geany/issues/3666#issuecomment-1972693169. The test is:
Copy a very very long text. Open a new tab in Geany. Activate in Geany in 'Document' the entry 'Line wrapping'. Then paste the text. The question is: Is the cursor in the visible area, yes or no? If no is the answer, then the issue still exists.
So I did this in FeatherPad: Copy a very very long text. Open a new tab in FeatherPad. Activate in FeatherPad in 'Options' the entry 'Wrap Lines'. Then paste the text. The cursor does not disappear.