There is a way to delete all lines between two particular line number.
Press CTRL + G. Text input will appear.
Go to last line you want to select by typing :line_number. For example :400000
Press ENTER to set cursor on this line
Edit > Mark > Set Mark. Circle near line number will appear.
Press CTRL + G. Text input will appear.
Go to last line you want to select by typing :line_number. For example :200000
Press ENTER to set cursor on this line
Edit > Mark > Select to Mark. Large selection will appear.
Press DELETE
https://stackoverflow.com/questions/67724573/how-to-delete-multiple-lines-by-line-number
There is a way to delete all lines between two particular line number.